A job advert popped up on therecently, searching for a senior software engineer to work at Decisive Games on "the next installment in a beloved strategy game franchise".
Considering Microsoft don't own the rights to too many strategy series that you'd call "beloved", the only one that springs immediately to mind is classic RTS Age of Empires. Might that be what Decisive is working on?
From the looks of it this appears to be a brand new studio, as there's no background to dig into regarding previous projects. The last entry in the Age of Empires franchise was the MMORTS, which came to a fairly ignominious end when the servers were shut down last year. Before that we has Age of Empires 3, way, way back in 2006. The series is long due for a revival, in other words.
The job role advertised is a very technical one, so there's little that can be read from the job requirements as to what kind of gameplay to expect from the mystery title. We'll keep our eyes peeled for any further information.