It's not Spoiler to say that one of the last things seen onscreen at the end of Iron Man 3 was a single line of naked text: "Tony Stark will return." The thing is, people want to know how and when, and though an appearance in Avengers 2 seems assured, it is - at least - possible that we might not have to wait that long.
Presently in negotiations with Marvel for a new deal, Robert Downey Jr. is apparently open to a cameo appearance on Marvel's possible TV series, Agents of S.H.I.E.L.D.
Said RDJ about showing up as Stark in Avengers director Joss Whedon's spinoff TV series:
“You know what? There’s no telling. I am open to everything.”
It would be nice to see Downey return to TV (he previously starred on Ally McBeal's 4th season, guested on Family Guy, and appeared as a cast member on SNL in 1985), and it's fun to imagine Tony Stark and Agent Phil Coulson bantering together once more; however, this all seems a bit unlikely, doesn't it?
For one thing, while Downey didn't shut down the idea of a guest spot on S.H.I.E.L.D., it seems unlikely that Marvel would want Tony Stark's next appearance to come as a one-off on a TV show - especially after the way that Iron Man 3 ended. I won't get into spoiler territory here, but there are things that require explanation and they likely couldn't, wouldn't, and shouldn't be explained in that forum.
That doesn't mean that it is an impossibility, though. Nothing is impossible should this throwaway comment - said in the midst of a laborious and lengthy press tour - somehow evolve into something tangible, but according to Marvel Studio Chief Kevin Feige, it doesn't sound like these are the kinds of stunts that the S.H.I.E.L.D. team (Joss Whedon, Jeph Loeb, etc) want to rely on constantly.
“If that works the way everyone expects it to work I think that would open up another avenue, another outlet for some of those characters,” Feige acknowledges “Maybe they guest star, I don’t know. I think they’re avoiding the cameo of the week on that show, which is very smart.”
Feige was answering a question about the possibility of using Agents of S.H.I.E.L.D. as a launch pad for unused Marvel characters - a roster that has recently grown with the return of Daredevil and also The Punisher, Blade, and Ghost Rider to Marvel's control - but it would seemingly apply to existing Phase 1 and Phase 2 characters as well, like Tony Stark.
That doesn't mean that every Marvel character should be considered in play, though. A TV show is not a comic book - logic, believability, and availability play a part in the equation. I can't imagine that Thor will ride a thunder bolt down to fill out some paperwork for HR, or that Agent Coulson will de-brief Blade, but some characters like Stark, Hawkeye, Black Widow, and maybe Daredevil could work in small doses. This assumes, though, that Downey, Jeremy Renner and/or Scarlett Johansson are game, and that Marvel wants to debut their new Daredevil in that format or ask people to stomach more re-castings.
That Feige is open to cameos - but obviously not eager to base the show around them - should surprise no one. It would be foolish for anyone connected with Agents of S.H.I.E.L.D. or Marvel to reject the notion of high-profile guest spots because - above all other reasons - this is still a prospective project that hasn't yet received the pick-up from ABC that we all feel is inevitable.
Once that pick-up is assured, though, it is easy to assume that this chatter will continue, but ultimately, Agents of S.H.I.E.L.D. is going to live or die on the way that it presents any lesser-known heroes. Sure, we may see a familiar face from time to time and other obvious nods to the link that exists between this project and the Marvel Movie Universe - but really, doing too much of that seems like one of those ideas that is better on paper... namely the kind that they make comic books out of.
Keep an eye on Screen Rant for any future Agents of S.H.I.E.L.D. news.