Performance:
I never tried it myself, but there is a youtuber that tried it out and made fair number of videos showing it off, together with other mods and such, and he always had a very solid frame rate with it.
Having said that, his frame rate only dipped when there were too many effects going on, usually (from the mods he was testing it with).
You can check his DX11 videos here:
https://www.youtube.com/c/314Reactor/search?query=dx11
Epic:
He never really clarified what happened that led him to cease to release new versions for UT99, even though he was asked what happened by folks with direct contact with Epic such as Anthrax himself, with the intent of potentially help him out.
Due to the way he behaved when asked, completely brushing aside the question, and the fact that he deleted almost every comment asking what happened, the general consensus of the people involved in trying to understand what happened is that he was never in fact contacted by Epic at all, and he had other more personal reasons that he doesn't really want to disclose.
We can only speculate, and my own
personal opinion is that he stopped doing so because maybe some people in the community, which he dubbed "Epic" (
not actual Epic itself) didn't really like what he was doing with this renderer, based on the wording he used to justify why he left.
Some people, like myself, didn't really like the over the top effects he was putting on pretty much everything, although some other people loved it (like the aforementioned youtuber).
And sometimes when the DX11 became a subject of conversation in Discord and other places, some people would openly say they didn't like this renderer because of all the unnecessary shader effects (reflections everywhere, bloom everywhere, tesselation bloating every model, etc).
But overall, as far as I could see, no one was really very vocal about it at all one way or the other, not even myself (I gave my honest opinion to others, but only when asked), and personally, while I didn't and still don't like this renderer myself as something to use in the game normally, I still considered it to be a very interesting project nonetheless, and could be used to do some experimentation on the visuals of the game.
So, maybe he read some of those, thought people didn't really like it, so he quit updating for UT99 out of spite.
Maybe he even read my own comments about it at some point (the fact that I said I didn't like it when asked by someone else), and considering that he took my mod into special consideration due to the tesselation not really working well with my models (not only my mod, but some other mods as well), maybe he felt attacked and felt it wasn't worth the trouble to keep updating the renderer with all these special considerations if the mod authors weren't happy with it (which again, he may have dubbed as "Epic"), and maybe that's why he doesn't want to tell the real reason to anyone.
I spent a bit of time thinking about this back when he announced that he was quitting updating it for UT99, and this is the overall conclusion I reached, but please note that it's entirely speculative solely based on what he said and the way he acted at the time, in other words, this is just my interpretation of it (and it could be wrong), and no one really knows for sure.
So, there you have it.