but as you say if the market and users dont value it. they just wont use it.
people will just make something else that can be of value.
satoshi did it..
Look, the users will value it if it is called bitcoin. You see, if you ABSOLUTELY want to ride a Toyota, and the ONLY car Toyota is making, is one with a digital speedometer, while you really want an analogue speedometer, you have the choice between not buying a Toyota, or buying their car with a digital speedometer. But as long as there is no competition, Toyota will force the digital speedometer onto you. There's no way you can force them to make cars with analogue speedometers, if digital speedometers are much more lucrative to Toyota.
but then you just dont buy it. and suddenly toyota lose customers.
Yes. But if the only brand you care about is Toyota, you'll buy the car with the digital speedometer.
If tomorrow, segwit is activated, do you really think that people are going to dump all their bitcoin in the market because they preferred BU, and run to the nearest altcoin ? Nope. They'll cope with it, because there's nothing else that's called "bitcoin".
So if miners, and miners only, decide to switch to segwit, and they do this with 60% of hash rate, then segwit will be. And all BU nodes will upgrade to segwit, or they will be useless. And people will continue using "bitcoin" as it is now.
Because there's no other bitcoin.
Even if 80% of non-mining nodes is running BU. They'll switch quickly. Or have disfunctional wallets.