>Natalia Romanova appeared briefly in CSI:NA, taking custody of Yelena
>Belova (or involved in some capacity, at any rate), if memory serves.

Hulk, Thor, Ironman, and Black Widow are 80% of the Avengers from the first movie - the only one missing is the less-interesting Hawkeye. They all know UF Gryphon. If the illustrious staff of Eyrie Productions are sending all and sundry against Oriphos to reclaim the lost children in a future installment, adding the Avengers to the team would certainly be feasible. Of course, that would turn the snark level to 11 - imagine Nall and Tony Snark (er, Stark) in the same scene. Danger!