I know a couple years ago, Stallone was talking about making a Rambo movie where Rambo would have to help take out some kind of alien creature on the loose, Predator style. But a lot of fans rightfully pointed out how weird that would be to suddenly toss sci-fi elements into the Rambo franchise, so I think they dropped it.
Another Rocky movie seems odd to me. I thought the last one served as a good send off to the series.