If you want me to give you a serious answer, how about SRAM support? It would be neat to save my progress in various games.
While probably not the most important, optional emulation of the TMSS would be a nice little touch. Could probably even write a custom bootrom for you.
Decided to start using this emulator since there was some weird bug with Windows not allowing me to associate .gen files with Blastem. So far it's very nice. I like that hovering over a tile in the VRAM viewer tells you the ID, that's saved me a ton of time. Would be nice too if along with the tile ID it showed the base address of the tile. It'd also be nice if the debugger windows were external windows, since I don't usually want to be using fullscreen mode. There is an inconsistency with how sound fading takes priority in Sonic 1 works between hardware (and Blastem) and clownmdemu. However my code is extremely janky since I wrote these menus from scratch and by the time I finish my project it won't be an issue, I hope.
