How many characters do you think we'll get in each DLC pack? I'm thinking they'll go with 4 or 5 - not too much work but just enough new content to look like effort to justify the money they're charging. This way they can recycle NPC characters into playable characters like Jessica Jones, Cyclops, Colossus or Beast (I'm going with the unplayable X-Men staying unplayable unless I'm proven wrong), but allow for surprising new additions. That'd would, for example, allow for the F4 plus, maybe, Dr. Doom as playable.
The X-Men portion would be meh unless Cyke and/or Colossus are unlockable, leaving room for more new characters. Like Dazzler, Spiral, Silver Samurai or anyone that will let me recreate Konami's X-Men arcade game or Capcom's X-Men COTA.
12-15 new characters for a season pass would be decent. I'd like more than 20 in the Pass, but I'd be expecting a Expansion Pass 2 over that.