Speaking as someone who has very minor 2D vector experience, I can’t say i’ve had any particular problems with Inkscape but i won’t doubt the problems exist.
I like your ideas. I didn’t notice you couldn’t delete vertices…that’s pretty important for any serious vector graphics. I suppose i haven’t done more than just push them around so far.
On the subject of pushing multiple vertices, i fully agree. I don’t know what programming would be required, but from an interface perspective the existing “Size” slider could manipulate a circle around the cursor which gives a visual hint of the cursor’s influence on surrounding vertices. Right now it seems like multiple vertices are forced to move together, if they are very close together…it makes it nearly impossible to move just one vertex in that case. I’m guessing if that’s the case then there must be some sort of threshold already built into the program, which perhaps can be manipulated at runtime.
I really like the ability to create arbitrary color blends in a single shape…it seems to be unique to Pencil.
On the subject of auto-smoothing, i haven’t paid much attention to it yet. Personally i am more concerned about the way the curves appear to crimp. It almost looks like the way a vector brush creates a shape rather than a line. I wouldn’t have any issue with this, if it were in fact the brush tool doing it, and if it were in fact a shape rather than a line. Vector lines should, in my opinion, be of uniform width from end to end, unless you happen to change the miter.