Gears of War was developed by The Coalition, which is a first party studio by Microsoft tasked with handling the IP. The first game by them was a great debut for the studio but it played it too safe in term of offering new and innovative gameplay, which might have ticked off some of the fans.
Recently, a rumor suggested that The Coalition might be working on a third person Perfect Dark game for the Xbox One, however they were only helping with the project. Storylab Productions has helped The Coalition with their work on Gears of War 4 and Gears of War Ultimate Edition, and according to an update on their official website, they might be working on a brand new IP with them now.
While Gears of War 5 is highly likely to be in development, a new IP as a separate project is an interesting prospect to consider here. Since Storylab Productions hasn’t worked with The Coalition on an IP like Perfect Dark, they can also consider it a new IP for them. This is, of course, if the rumor is indeed true and Perfect Dark is being resurrected by Microsoft.
Gears of War 4 was released back in 2016 and this project has been in production since 2017, so it seems to be still in early development and we might have to wait a bit before we get an official announcement for it.