Partly thanks to all the details that have had to be figured out in the wake of Disney taking over Fox, it's been a while since we've heard anything concrete about a third Deadpool movie. According to Deadline, writing team and sibling pair Wendy Molyneux and Lizzie Molyneux-Loeglin are on to craft the script.
Star/producer Ryan Reynolds has been taking meetings with various writers to hear pitches for a potential third film, the first that will officially be produced by the Marvel team and fit more squarely into the MCU, even though it'll still be its own beast. It'll reportedly still be R-rated across the pond (both the previous movies were 15 in the UK), which means Disney will have to find some way to release it and a home for it once it his home streaming (the rating means it'll more likely end up on Hulu than Disney+).
Also unknown right now? A director. Deadpool 2's David Leitch may be too busy to make the movie (unless development chugs on to the point where he's available again, and he hasn't been involved in finding writers).
The Molyneux duo scored the gig by impressing Reynolds and the executives, and we can expect the script to evolve as he gets involved. The pair is best known for TV 'toon Bob's Burgers, and are behind a new series, The Great North, which will debut in the new year.