You're probably right on most accounts, but on Sony's approach on not caring I know I'm right. Sony could've easily not only convince, but even coerce companies like Activision or Squeenix to fork over their characters. Sony's gaming division alone is infinitely more powerful than any IP holder in the gaming industry (save for monsters the likes of Nintendo and Microsoft, of course). The game was just minor experiment for Sony.
Do you seriously think Sony would pass up the opportunity to make another potentially huge franchise by not adding 3rd party characters people wanted? Sony may be powerful but it certainly isn't perfect.
In any case, while it's true that known faces could make a sequel (which I honestly don't see ever happening) very successful, there are a lot of fundamental flaws that make this game a broken mess. Such flaws need urgent addressing. So no, famous characters aren't the only thing this game would eventually need.
They're definitely going to have to make sure it's more balanced (or less broken rather) but being that this is a crossover game, the characters will be drawing more attention than the game's balance that they got plenty of time to make a good patch after it's released. --- Mortal Kombat vs. Street Fighter Tekken vs. Dead or Alive, Shonen Jump vs. Capcom please