Mark Ruffalo, the current Hulk in the Marvel Cinematic Universe is enterained by the idea of having a live-action Planet Hulk movie having this to say:
Mark Ruffalo: “I think there’s a lot of places to go with him [Hulk].”
Scarlett Johansson: “Like where?”
Ruffalo: “Well he’s going to space. Yeah, I mean there’s some talk of maybe Planet Hulk.”
IGN: “Would you like to see that?”
Ruffalo: “I’d be completely interested in entertaining that.”
However, Mark is not currently in any talks at this time to play any further films starting The Hulk other than the Avengers films so we will have to just wait and see if Marvel decides to add it to their upcoming film list.