Great post!
I love the approach.
I come from Maya and Cinema4d a lot of the tools you suggested are already there, so I think the 2d world needs to catch up.
I use AD mostly to draw vector files to be laser cutted on various materials.
Windows and Layers generally for me are not annoying.
Curves.
I totally dig the idea of having more control over the curves, also, I'd like a way to modify a tangent and have the other tangent to mirror the behaviour of the first. So, whichever tangent I modify, they'll always be mirrored.
Improved welding tools would be great, too (the ability to paint on n vertices and have them welded, like ai). Another useful thing could be merging: I pick 10 vertices and I want to merge them to a single one to their center.
Plugins
This would be awesome. Give us the APIs, give us JS and Python as choices, and you will se how many plugins start to grow in a very short time.
This could also open the way to all artists working with coding (I'm not an artist but I love working with code for creating generative works).
Cloners
Oooh, I need this so bad.
In Maya I can draw with curves and have them mirrored as I modify them. So I can draw half of a face seen from front and visualise all the face (right half, left half) as I draw.
This would really be a killer feature, since you could create lots of different patterns by mirroring not just left and right of the current canvas, but also top and bottom.
Parametric
Pure awesomeness. But probably too much for AD. I use Fusion360 often and it's one of its features that I appreciate most.
Maybe having some constraints would help (EG: set the minimum distance between to curves or to points, so that when you move one you move also the other).
Simulation
Cool, but not on top of my list.