In fact the example provided with Resolve 17 beta IS actually an x264 encoder. On the first sight it seems they provide raw video data and you can feed the encoded frames back to resolve so it can mux it with the audio streams.
Personally, not being restricted to the limited options they give you but having custom x264 settings would already be a big plus in my book.
It's a shame that a full set up like in Vegas or Premiere might not be possible, but better than nothing provided the work isn't too much.
Thanks for the heads up.