Sir Ben Kingsley announced a few weeks ago that he was working on a secret project with Marvel. Seemingly playing The Mandarin in Iron Man 3, that film revealed that Kingsley's character was actually an actor called Trevor who was being used as a front for the whole Mandarin ideal. Many fans were in uproar about this, and it most definitely divided opinion.
In terms of the 'secret' project, Kingsley recently said,
"It's a secret Marvel project. I'm not allowed to say any more, you're going to have to wait and see."
Of course, with the way that Marvel Studios is constructing its universe, many presumed that this project could well be a 'one-shot' short film, similar to Item 47 and Agent Carter. Well, according to Latino Review, if that was your guess... you were right.
LR is claiming that Marvel have apparently seen the error of their ways in what they did to the character of The Mandarin in Iron Man 3. So much so, that this one-shot is to be their way of making it up to fans. It's claimed that the short will see the real Mandarin furious at Guy Pearce's Aldrich Killian and Kingsley's Trevor for making a mockery of the Mandarin identity. Yes, the report claims that there will be another version of The Mandarin.
No more is known at this point, but what we see of The Mandarin in Iron Man 3 definitely varied a lot from the comic-book version of the character that we've seen over the years.
In terms of a pay-off down the line, i.e. the real Mandarin takes on Tony Stark, that's literally years away... if it happens at all. At present, there are no plans whatsoever for an Iron Man 4, and Robert Downey Jr. is purely signed on for Avengers: Age of Ultron and Avengers 3.
Expect more on this as it becomes available.