Doctor Strange is set to be a bit of a unique Marvel movie when it lands in November 2016. Not only is it focussed on a single characters (something that's increasingly rare) but it also exists in a world of magic we haven't really delved into before.
The latest rumour suggests that we might see a familiar face in the film in some capacity, even if its just in a credit sequence. This is entirely speculative at this point.
Well this podcaster thinks he has a scoop and it could end up being true- Robert Downey jr gets around in his role as Tony Stark and it's only a matter of time until he gives up the role so Marvel might as well get as much use as they can out of him.
Naturally this could be a post credit tease or even a very minor appearance in passing, time will tell. One thing is for sure- fun secrets are pretty hard to keep in our modern world.