I've been a game developer for over ten years, and I'd certainly invest the time necessary to ensure the peripherals owned by the vast majority of my players will work rather than require that people buy a new console, my game, AND a new stick. Especially if it would take, say, less than a week of work...but I can only even invest that time on the single console that gives me the option to have older sticks work.
I would also advise any company I'm consulting for to do the same - a bigger playerbase is never a bad thing, and you're more likely to sell a copy of the game to someone who can use an input device they already own. It's easier to stomach a $60 or $20 game than a $200 stick.
That's not to say that there are game companies run by people who don't think that way, but they wouldn't continue to if it indicated they may lose money. If SG2 were to support this and SF5 didn't that would be news, and at the very least I'd bet SSF5 would add it.
