Lionsgate has secured major rights from Millennium Films for the Rambo and Expendables franchises. They will have global distribution rights to the upcoming Rambo prequel as well as lead production for any Rambo-related TV shows. They also have the rights to develop and produce Expendables movies, TV shows, video games and other (but not necessarily true sequels).
Expendables was a good idea they never really delivered on and the last two movies pretty much tanked it. I don't know what's stopping another studio from gathering a bunch of over-the-hill action stars for their own movie where they're not mercenaries running around like they're all in their 30s. Would be a lot easier to get Tom Cruise, Matt Damon, Liam Neeson, Vin Diesel and Keanu Reeves for Original Movie 1 than Expendables 5.