An "offset blur" control doesn't quite make sense from technical point of view. I understand your idea. The thing is, blur is not a independent property of an object--it's a filter and if you modify the object the blur will change to reflect those modification. So if you want to offset the blur, you have to offset the object. In which case, you don't want a "blur offset" slider, you want a "offset" slider which would do exactly what you had in mind without having to be dependent on the use of blur. Now the question is, does Inkscape need an Offset slider when it already has Dynamic Offset? Certainly a slider makes it more accessible, but there are hundreds of controls that could be promoted out of the menu and given their own slider, but then we won't have any room for the canvas

I feel the same about the blur slider also. To have such a prominent position on the UI I think the average artist needs to use it for 20% of the objects in a drawing (That's just my own idea of a percentage). Some artists do indeed use blur far more often than that whilst many other artists never ever use blur. So, how many artists use dynamic offset intensively enough to give it its own slider in the GUI?