UPDATE 18th February 2016: Capcom's said it'll address Street Fighter 5's rage quit problem.
The publisher told Eurogamer today players can expect a change, but we still don't know what system it'll use to punish those who quit matches early - or when it'll be added to the game.
"I can confirm that it is something we are going to be addressing to make the gameplay experience one that all fans can enjoy and be rewarded fairly for," a spokesperson said.
ORIGINAL STORY 17th February 2016: Street Fighter 5 does not punish players who rage quit.
If you quit out of a match before the game has had a chance to report the results to Capcom's servers, you won't register either a loss or a victory.
I've spent the morning testing this out, and can report that if you rage quit a match, as far as Street Fighter 5 is concerned, it never happened.
You can check out recently-played matches in the game's Battle Log, found within your fighter profile. Here's what it looks like (I'd rage quit the previous match):
Even win streaks remain if you rage quit. Here's a screenshot of a match I played after pulling the plug early in the previous ranked match (note my win streak, listed at the top left-hand corner of the screen, remains):
This isn't a big deal for casual matches, but it is for ranked online play. It means that, currently, you can prevent yourself from slipping down Street Fighter 5's league system. Of course, if you keep rage quitting you won't climb the ladder either, but the problem is serious enough for players to have called on Capcom to address the issue.
The Street Fighter community has spent the last couple of days coming up with ideas for how the game should deal with those who rage quit. Ideas include automatically losing the match, which probably should have been in the game from the start, dumping those who rage quit often together in the same matchmaking pool, locking rage quitters out of online play for five or 10 minutes, and forcing repeat offenders to play the awful tutorial for an hour before they're let back online. That last one's a joke. I think.
Thankfully, it appears that Street Fighter 5 online isn't rife with rage quitters; I've suffered only a few rage quits so far this morning. But Capcom will want to jump on this as soon as possible to prevent rage quitting from blowing up.
Oh well. Here's that video Aoife and I made about Chun-Li's boobs.