Multiverse + FM-Towns Joypad
I got the game on cartridge - nice game, don't have much time for games but Multiverse was most played in 2019 
and i would like to play it with extra buttons with JoySNES but bothering with dumps is annoying. Which makes me think that for such a cases there might be a hardware solution developed - say, you insert a "patcher" into your MSX slot, then insert a real cartridge into a "patcher", and it will change the data read from cartridge at some addresses configured (flashed out to "patcher") before. Shouldn't be too complicated with FPGA (the only thing is that "patcher" probably should have a flatcable, because stacking cartridges one on other is inconvenient, so maybe the whole project could be based on MSX-Flex)
Just an idea. Also it could probably also incorporate some more features - f.e. changing port number - imagine you have two Wozblasters and would like to have second one work on ports C0-C3 (like DalSoRi which can be switched to those ports) - and you configure "patcher" to proxy any C0-C3 I/O to C4-C7 into the cartridge
