I have written my own game for the original game boy[1] with the goal of bringing very modern tetris (Think Tetris the Grand Master) to a retro system. It's free and open source. Though the sound seems to not work well on the emulator in parent. I've tested it on real hardware and it is definitely an emulator bug.
I see these retro emulators pop up from time to time, but I just don't have the time to really check them out (or the discipline to realize always an addict looking to avoid relapse). I know that there are "complications" about the ROMs to use in the emulator. However, is there a scene of people making ROMs of new games specifically for playing in these emulators? Are the game devs that are making modern games for retro systems that would be free of the "complications"?