I think that (and I could be wrong) the PP meant US can't expand the roster of Marvel Characters in the park.
The contract might give them the rights to the characters they had at the time, in the comicbook designs of the era...but as I understand it (and I'm also not a lawyer) they can't use any characters that weren't in the original agreement, or use any of the newer looks to the characters they do have.
So I don't think they can build a new ride themed after a character not in the original contract.
And considering the rumored rule handed down at Marvel regarding the restrictions placed on writers of the Xmen titles about no new characters, no cross-overs that could expand the Xmen character roster for Fox movies...I think Disney will be quick to stop any Universal parks attempt to grow the Marvel presence beyond it's current roster.
Correct