I’d love the ability to create simple maps about as fast as I could draw them on grid paper. That means good drawing tools, perhaps focused entirely on one style. For example, a system where you could draw rooms with rectangle, polygon, and ellipse tools that would then rapidly render them in a style like Dyson’s (https://dysonlogos.blog/maps/) or other sketch-looking, way would be fantastic. Especially if it could be done real time as the players explore.
Maybe provide, or sell, just a few drag-and-drop symbols for chests, traps, etc in the same style as the map. I imagine you could even hook dynamic lighting into such a system without having to draw overlays on another layer.
All the VTTs I’ve seen focus on letting you import bitmaps to create your own tiles, and make very detailed and pretty maps. This could be a differentiator, plus a lot (ok, at least just me) of people like to have very simple stylistic maps like this so that most stuff can still be in the imagination.
UPDATE: I just found Gridmapper. Click the link at the bottom of the page to view the demo. This feature request is for some thing like that, except that it (maybe) creates dynamic lighting maps and, of course, results in a playable area in astral.