Save state conversion/better save state compatibility in Retroarch?

[nl255]

I was wondering if there are any good NES/GB/GBC save state converters to make them work better with Retroarch or if better state cross compatibility is planned in the future. I had to switch to Retroarch because that is the only way to use the Genesis Plus emulator but unfortunately that means there are several games for other systems that I just stopped playing because there is no apparent way to move the state data over (sadly said games don't even offer a password save).