I think not having a truckload of broken characters would help: e.g. vanilla Cyrax, vanilla Kabal, vanilla Superman, vanilla Black Adam. The corollary to that, though, is that machine gun patches are an awful idea because they deny the game the chance to grow. I really think that the testers and the quality control department will have a huge role to play in the life of MKX: we know it's going to be fun, we know it's going to be successful but whether or not it's elevated to the pantheon of truly great fighting games, like Tekken 3 or various SF titles, depends on if the initial balance is somewhat competent because the two extremes are equally bad.
If the characters are broken and overpowered, no amount of 'learn the MU' will help: I'm not talking vanilla Deathstroke or Killer Frost, I mean vanilla Superman who reduced the game to eye laser and F23. Ditto Cyrax, who had more infinites than Sheeva had combos. You can't just ignore the problems a game has in that state On the other hand, firing out patches every week isn't going to help because it denies the game the room to grow. If I had to choose, I'd say having overpowered characters is the lesser of two evils because we know NRS games always finish their lifespans with a few massively overpowered characters: Kabal, Cyrax, Kung Lao, Kenshi, Sonya, MMH, Aquaman, Batgirl. But if NRS can hit a balance and a somewhat competently balanced game to give it the room to grow, MKX could be something very special indeed.
It'll also help if NRS don't listen to casuals. I know they buy more copies as a market than the likes of the serious players, but how many of them will still be playing it when the new COD or FIFA or Madden drops? They'll leave once other people level up and their cheap shit doesn't work anymore so if NRS just ignores some of their more butthurt complaints: Deathstroke's guns, for instance, while annoying as fuck, made him a good character, not broken. Raiden's teleport, while annoying as fuck, made him a good character, arguably top 5, but nowhere near as broken as Cyrax.
Personally, I'm dreading that we'll get a gamut of patches initially: if Erron Black is in and has a gun variation, expect the nerfhammer