Meshed has said the following about switching to Unreal:
"Never going to happen. Some of the highly optimized things VaM needs to do like specialized skinning and physics would be quite difficult to make work in Unreal. And I now have nearly 8 years of experience in Unity and C#. That won't translate very well to Unreal."
"And you mentioned MetaHumans in Unreal. MetaHumans have no genitals. There is no grafting system like Daz3d to add your own. You would have to completely modify the mesh and re-rig."
I recall reading that systems like Lumen, which make static environments look really good, don't work particularly well on dynamic human models. And Vam, is really about how good the people look, not how realistic the backgrounds are.
Also note that how good you can make a given model/system look with full rendering has no bearing on Vam, where each frame needs to be rendered in realtime.