BIP 148 (aka UASF) is not accepted by pretty much all developers. It has not been accepted by Core nor is it likely to be accepted and implemented by Core. As of now, the segwit implementation in Core is as is specified in the segwit BIPs, which do not include BIP 148.
So it's now stalemate from 2 directions at once?
Wouldn't it make more sense for the devs against BIP148 to quit Bitcoin altogether given that attitude? Once a different cryptocoin implements a successful 2nd layer, Bitcoin will lose a significant competitive edge. There's nothing magic about contributing to the Bitcoin codebase, another team could implement Segwit and other future technologies without them.
Why continue to be a part of a project that's being prevented from progressing? The devs are going to run out of non-fork improvements and maintenance coding (for the most part). I'm seriously considering looking at why I'm still involved at all.