Nah, people have the rights to enjoy Final Fight in their favorite platform. It doesn't matter if it is from 30 years ago, or why would translations even exist? People should just learn japanese and new languages, under that mindset.
Besides, the SNES 2 player hack was done already (by two different programmers at almost the same time, no less), it is not finished yet. There is also the Final Fight 3 players hack for the arcade board.
My point, that maybe got lost somewhat, is that if you want to play Final Fight with two players, the arcade and Sega CD versions are sitting there and are both arguably better than the SNES in every other respect, too. Your comparison with translations isn't entirely accurate: if a game was localised from Japanese to English, I would very much rank that as a low priority. It's not a case of saying "why would translations exist", it's a case that if you're going to go to the huge effort to translate a game, maybe do one that hasn't already been translated. Therefore, if you're going to make an effort to hack a two-player mod, maybe do one that doesn't already have an even better version available on two different platforms (and yes, a SNES classic is still an emulator, so the 'original hardware' argument doesn't work either).
Anyway, the three-player arcade mod IS a great idea, since that's unique. Honestly, people can hack whatever the hell they want, there's no need to get annoyed about my opinion.