I don't think it works like that, it's likely a result of Marvel & Fox's improving relationship. In the case of Marvel Future Fight, it's an ever-evolving game where they can jump on-board ASAP. MvCI, as I said, likely had its base roster nailed down 2 years ago, & the 2017 Character Pass probably around a year ago.Who knows, maybe this has been in the works for a while? Maybe MvC:I was the game that convinced them to do the same for others?
Any theory I can think of that means Psylocke is there day 1