Looks like Age of Empires is next in making the jump to Unreal Engine. Recent job listing for World's Edge has a requirement of:
"6+ years of professional experience in AAA scale Unreal Engine game development"
Not really surprised since all 4 remasters just used updated versions of Ensemble's proprietary engines, AoE 1 and 2 using the Genie Engine and Mythology/AoE 3 using the Bang! Engine. Then AoE 4 used Relic's proprietary Essence Engine.
I guess this also means Relic will not be making World's Edge next game as well. Also, the job listing having "AAA scale" is interesting. I don't think RTS games have been considered "AAA" for like 20 years now.