Tilemap rendering and camera support without having to write your own (unless you need fancy stuff like split screen). Basically, a function that would offset all drawing operations (unless you set a bool to ignore the camera when passing an array to e.g. handle the HUD) by certain x/y.
Also, unless it's already there, a top-left coordinate system. Many new devs may come from engines/framework that use it such as various "fantasy consoles" such as PICO8 or TIC80. Bottom-left or center coordinate system may confuse them a lot.
//edit: Also, could we get SVG sprites so they won't pixelate or blur no matter how much we zoom in?
//edit: Another one: A ready to go IDE, possibly Eclipse-based would be nice so you don't have to use several different tools to get what you need. Also, it would allow for stuff like auto completion (a.k.a. intellisense) to be possible (no more typos, yay!)