They should use GGPO, problem solved, no excuses.
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I love this tired ass response. You think NRS doesn't know what rollback netcode is? That they've somehow missed the endless cacaphony of GGPO nazis that turn up in every netplay thread for every game.
This would solve almost everything.
But instead NRS is making their own netcode system w/e reason. They're going through tons more trouble to meet the expectation of GGPO.
Sad truth; GGPO / RB requires a COMPLETE design commitment from day one (if you want it done right). Audio, Graphics, Inputs, EVERYTHING has to go through the GGPO monster as the game runs. It is ideal for games that are either non-resource intensive (emulated, or you know, dive kick) or running on a brand new / freshly gutted engine (KI, SFxT, IG ports). Given there is NO way the existence of GGPO technology has escaped NRS' field of vision, there are only a couple possible reasons NRS hasn't implemented it yet.
1) It's too hard, it costs too much, it would take too much time.
These are all publisher problems, but gutting the MKX engine within the allotted development window is an arduous suggestion to say the least. It's going to take money, and bodies, and time and that doesn't guarantee NRS has someone on staff who can actually do it. Even if everybody at NRS says its a good idea and is willing to work on it and is capable of delivering, there's no guarantee WB won't just say, sorry, too much effort, we ship with the online we have.
2) Their engine won't support it
MKX runs on their 4th gen revamp of UE3. I've never heard of a rollback UE3 game. I think maybe Arkham Gangsters or whatever that shooter was called did it, or maybe that was Friday Night Arena or whatever. Either way. I know Halo, CoD, Assassin's Creed, GTA, Battlefield, and several other huge titles don't use it. It's hugely low % technology and it may just not work with UE3.
3) It compromises their vision
NRS prides themselves on exceptionally high resolution games that run at 60 fps without fail. It's a selling point. Its on the box. Meanwhile, GGPO is a system hog that runs well in 2d games and emulators. I can assure you if even Boon himself said to his WB masters, listen we can have frame perfect (or close to) online play but we can't do 1080p/60fps at the same time or we have to downsample the audio or worse, it occasionally crashes; It will get shot down.
4) Nobody (who matters) cares.
What the GGPO FGC crowd always ignores is that they are literally the 1% of gamers. They are literally the smallest market, the subset of offline players inbetween or without locals + the subset of the online masses who are actually willing to drop online play over a few frames of lag. And yes, the vast majority of randoms playing fighters online do not care about missing 1 or 2 frame link to lag. You've played them, I've played them. They just don't. SF4 online thrives without GGPO, Marvel online thrives without GGPO, Tekken, Soul, Arc and everybody else, no rollback, no harm to sales. And when frame perfect online gameplay is a luxury almost NO other genre (or game) provides, you can't even call it a selling point.
So no, they are probably not going through tons more trouble to do it this way. This is probably the path of least resistance.