Majority hashrate + original blockchain = Bitcoin
Majority can only be economic
Economic majority doesn't mean shit unless they put their money where their mouths are and start mining. You could have 90% of all BTC and be completely unable to stop a hardfork because it's secured by proof of work, not proof of stake. And it's the hashrate that gives users the ability to trust the network. A minority fork is worthless because it's easily subject to a 51% attack giving users no reason to trust it.
An economic majority can push hashrate over eventually. Miners can only mine for so long while loosing money on a chain that's worth way less. I don't think UASF will actually succeed, but an economic majority could definitely render the hashrate before the split irrelevant after a month or two.
Note - if BIP 148 succeeds and the minority chain still exists, a large amount of the hashrate on there would probably be supporting BU, so couldn't they just hard fork on the legacy chain? Is that not possible for some reason?