There's no problem that could make bitcoin price crash unless there's block split but both of them have equal support from miner/community or there's big technical problem.
But, i don't see any reason bitcoin price will rise after UASF
It is not the UASF option itself that matters
It is what happens next after if gets activated (accepted). UASF activation would prove in practice that full nodes have power over rogue miners
once again, and thus the latter can no longer hamper or otherwise hinder Bitcoin development as they have been successfully doing for the last few years. The BIP148 proposal means activation of SegWit without miners' prior consent (or even despite their resistance)
From August 1st, 2017, miners are required to signal readiness for SegWit by creating blocks with the version bit 1. This will cause all SegWit ready nodes, which make up over 80% of the network, to activate and begin enforcement. Miners must also check blocks prior to their own and ensure that they also signal for SegWit, and only build on those blocks
Basically, miners are told to pack their things and go home if they disagree (provided this proposal gets accepted, of course)