I'm just looking through the Feature Requests and remembering which ones in particular I'd very much like to see. This is not a complete list.
object rotation - A set of quick and easy object transformations, like rotation and scaling.
Use DirectX quads instead of sprites - Given the impression that graphics will be sped up and it could be the stepping stone to 'object rotation' and especially '(non-model) 3D', I support this.
Angular Movement - Not so much the 'angular movement', which is extremely simple to implement by itself with enough knowledge of trigonometry (add a velocity vector <cos(angle), sin(angle)> to your position), but the non-rounding part. BYOND screwed that up in my opinion, probably in some kind of attempt at consistency.
Custom fields for bug reports and feature requests on hubs - A hub's Bug Report and Feature Request forums shouldn't have anything to do with the BYOND software or website.
A built-in vector datum usable by everything in the native pixel-movement implementation. It could also be used for the awkward sets of variables such as x/y/z, bound_x/y, pixel_x/y/z, bound_width/height, maptext_width/height, world.icon_size, and probably some more I'm forgetting.
Automatic, constant updates to the mouse's position on the screen relative to the player. This could be stored as a /vector, from the center of the screen to the mouse, or from the bottom-left of the screen to the mouse, or whatever.