Hello Anna, what a nice project!

What features I would like to see?
A whole new standard for vectror drawings.
Svg seems didn't got widely used for it's main task -graphics for webpages online,
rather by artists in need for larger scaled images outside illustrator.
Because of this, important parts are missing: covering the whole colour range -srgb vs linear rgb-, better colour support -cmyk, cms-, better handling of gradients.
Would be nice if you could choose how to interpolate colours between two steps in a gradient, and, all of it being pure vectors.
http://www.inkscapeforum.com/viewtopic.php?f=5&t=13764#p53418
As for now only linear exist through svg, and, it lacks to be displayed right in large numbers.

A better rendering method.
Svg may be fast to load and easy to manage by programs as the rendering is simply defined by the object's position in the codes.
That is, very painful at times, and close to impossible to be managed in others.
Also it would be nice to have more compositing options -like the multiply-.

So a redefining of the z order of the objects.
The ability to vary that for the rendering inside one object.
For example, drawing knots would require less tricks if implemented.
Also, reproducing a brushed texture on a stroke would be possible.
Like this approximation: http://inkscapecommunity.com/ic_gallery/albums/userpics/10014/3ff.png

There are Bezier-splines used widely but those doesn't seem to fulfill in many cases.
They are too intuitive to be used.
What I would like to have, is a curve that is based more on it's curvature, then the current handles.
For example, drawing a letter "S" nicely is very hard by hand right now.
Where would the inflexion point be on that curve? How would the radiuses of the curve follow eachother?
Spiro-splines may be a step forward in the look.
I would like to see a way to define line segments by their starting and ending radiuses -and curvature interpolation methods between those two values for the inner points-.
Also if those could be displayed in a live way, along the path, as well as their derivants.

Now these basic things were changed, it would be nice to have a C-stroke.
After the b-splines, being those C-strokes calligraphed strokes.
That is, the ability to assign pen shapes to each node on a core path in a live way,
with their transformation values being preserved and the program would render the pen shape's transition along the core path, with it's transformation values being interpolated.
The ability to change the interpolation method being used.
The ability to do those through a tablet, where like the pen pressure would affect the scale value of the pen shape.

Gradient meshes^2.
http://www.inkscapeforum.com/viewtopic.php?f=22&t=16091&start=25#p61150
With a new rendering method being given, it would be nice to have the ability to add new channels to the objects,
like a bump map -preferably drawn with a gradient mesh-, that would be then recalculated to be a normal map,
and used to define in which point of the shape, what to be rendered.
I'm thinking of using that feature to map a previously drawn gradient onto an object with a simple bumpmap.
Giving realistic 3D shading a boost, without the actual vectors being in 3D.
And to have it in a live way, that you could change the "light direction" and "material" by selecting another previously drawn gradient to be mapped.

A way to make dynamic blocks.
Right now you can draw *, circle and rectangle as a "dynamic block".
Well not being actually defined as a dynamic block, but they are working alike that feature.
To have the ability to add handles to a variety of objects "grouped" together, that would modify one data of the object.
Like this for example:
http://www.inkscapeforum.com/viewtopic.php?f=28&t=14049&p=55192#p55165

Vector based filters.
With fast rendering, and with a nice panel to edit the parametres.


Hmm what else could be improved. The handling of text objects?
That's for sure, however I would rather have the previously suggested features, than the ability to make texts without any problems.


Actually there could be other things mentioned, related to the original svg useage.
Like an environment for developing svg with css, and another for animations.

Edit:
Some less radical changes.

An accurate working engine. A way to the boolean operations don't affect coordinates of the path nodes that are nowhere near intersecting parts.

A snapping feature you could rely more. There are many cases it doesn't work, even if it is enabled.

An align and distribute panel with the option to align shapes onto a line not being horizontal/vertiacal.

Undoable-redoable selecting.
Preserving node selection when in "object mode" -like in blender.

mesh gradient.
a working filter editor.
post-processing the freehand tool. You need to know the smooth strength and the shape before you draw. It will be ways better to set it AFTER (or at will)
multiple fill and stroke for one shape.
style browser : choose between previews of object with different combination of LPE + gradient + filter
gimp/inkscape cooperation (unifying term/ui)
being able to simplify part of a path (and not the whole)

What happened to the original post?
Anyway.

Found a video on a similar thing to a "c-stroke" feature:
http://vimeo.com/49797030
Kind of like a style browser?

Last tread obviously have died (actually, I cannot find it anymore).

One issue with those kind of threads is that we all use Inkscape in different ways, and we all have different aproaches on how Inkscape should be enhanced, so to the end the thread would get pretty messed up by ideas, many of them may only benefit only one single Inkskcape user.

Personally I have this list:
1. There is a lot of bugs that should be resolved first. Personally I think that is way more important than implementing new features. The bugs I hate the most right now is: Doesn't print pattern along a line, Crashes when trying to print on some W7 computers, visible gaps between adjacent objects.
2. Better performance in general.
3. Better CAD capabilities (for pure CAD tasks I use Librecad) and that a circle is an actual circle and not just an aproximation.

Grobe wrote:3. Better CAD capabilities (for pure CAD tasks I use Librecad) and that a circle is an actual circle and not just an aproximation.

What do you mean by approximation ?
Circle should be perfect unless you turn it into a path (which could be done when exporting, I don't know) then a small error is unavoidable but the error should be small (<0,03%)
http://spencermortensen.com/articles/bezier-circle/

Quick test:
Draw a circle, duplicate it, and lower the curve distance from 360°.
Zoom in outlines only mode to the part of the arch near the end point.
The duplicant doesn't mach exactly with the original.

Though circles have a different tag in the codes, to me it seems the rendered part is the exact same as it's path equivalent (Ctrl+Shift+C).
As far as I see it the circle arch has it's nodes where they appear after converting to path although they are not displayed.
And, that the nodes are counted precisely, that segments don't match.

-Another quick test: draw a circle, then duplicate and rotate it a bit. The object won't cover each exactly.
To point out any further problems with the used mathematical model, add these two objects together, and see how many new nodes will be created in a seemingly random way.-

With a curvature based line definion, they should look all the same.

I get it wrong , I thought he meant inscape outputs svg that are inaccurate for "real" CAD software.

If the problem is with rendering circle inside inkscape thenI don't know precisely how it works under the hood ; it looks circle are converted to path before rendering on screen.
The classical algorithm turns a circle into a 4 nodes with some inaccuracies (which "could'nt be noticed" most of the time).

That what occured with current version of inkscape.
But in the dev release of inkscape I run, if the circle is large (vs page size) then its approximation get more nodes

What I really would like to see (some have already been mentioned):

- choose to set the stroke width inside or outside a shape at a click of a button;
- multiple strokes
- putting origin of coordinates in top left, or anywhere
- optimizing png export (reducing file size);
- ability to export to jpg without having to convert the png, with compression options; (useful when making designs that incorporate images, like certain webdesigns)
- better font rendering
- underline text
- cross document shape/object library
- cmyk support
- export object styles to css for copy/paste (and font styles too)

- documentation for making extensions (with visual examples); (or better - a Codecademy course!)
- make extensions' interface more sexy: more interactive (data in the extension's interface updating depending on other input fields, activating/deactivating fields when a checkbox is checked etc); ability to add images/icons in extension's interface; ability to better position/align input fields

What a great ability of writing this post contains.
Its been a true pleasure to go through your post. Keep up this good working.. ..