Wouldn’t it be easier to import Quake 1 map and convert Quake brushes into UE4 brushes? (Epic would still have to optimize BSP in general, but it’s a way less work than making whole set of BSP tools)
Trenchbroom was built by 1 very dedicated guy. It took years to get it where it is now. I doubt Epic has resources to do that (unless they just license the UI / workflow from Trenchbroom author). So maybe better run Trenchbroom / Radiant in parallel with UE4, and simply refresh imported .map inside UE4 to get updates?