Right now, it mostly looks like Mike Ratzlaff has built some of the Great Stygian Abyss from Ultima Underworld as a DOOM level using the GZDoom engine. Ratzlaff describes the video thusly:

This video is a demo of my project GZDoomUW Take Two, my attempt to bring Ultima Underworld into GZDoom.
This video introduces the interface and environment interactions.
There’s a whole lot of other feautres not covered in this video, there is a preview of some of them at the end of the video.
Funny thing, I started this video wanting to demo what I’d been working the most on – doors, containers, and passages, and then never got around to showing them off. Oh well, another video…

However, the ultimate point of these efforts is to re-implement Ultima Underworld within the GZDoom engine, as faithfully as possible. As such, this video is not so much a demonstration of the finished product, but rather of some promising early work on a much more ambitious project.