I would really like to see some collaboration between Tony Stark and Steve Rogers in the upcoming film.
Note, I didn't say "Iron Man" but rather Tony Stark. And we're talking like a 1-2 scene cameo, nothing more.
Perhaps a scene, where Tony is bouncing some tech ideas off Steve, similar to when Howard was showing Cap the shield variations in TFA.
Howard was a big part of Cap's life during the war, and it would be nice to see the start of a similar relationship with Tony, even if Steve shoots down all of Tony's ideas, in favor of "hard work, training and the basics".
Perhaps we could even see a "prototype" energy shield, similar to Skrull Cap's replacement at the beginning of Season 2 of AEMH.