I have seen a developer from Ninja Kiwi around on these forums, so hopefully he can give me a responce to if they are working on any of these features.
Scroll wheel compatibility with tower selection and menus. This is a bit much, but an option to switch between mobile and flash graphics Monkey City tracks (maybe in biome-specific packs buyable with Monkey Money). Windowed and Windowed-Fullscreen mode support. Add the Deluxe Maps (including the BTD4 remakes).
But while I am on the subject of things that seem a bit off, here are my suggestions for this game: I have heard rumors around the forum that those tracks are going to be placed into this version, but I am not sure how long it will take. Yet, the Steam version doesn't have all of the exclusive tracks in the Deluxe version. So this version of BTD5 is free if you have previously purchased BTD5 Deluxe, released about 3 years ago.