Even if UASF will create altcoin then be it.
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I will use BTC as store of value and UASF to play casinos, pay for stuff. Same time let original BTC be original BTC.
You don't have a clue. UASF won't split it's a softfork. Some stupid miners like jihad and BTU bovine can ragequit and create their altcoin BTU, but it will be just alt like LTC, no more
The main point of UASF is to begin SegWit before it gains a significant majority of miners. If, when it occurs, SegWit has a minority of hashrate, there will be a split.
It could get very complicated if BU or neutral miners are particularly determined to stick with their chain. Therefore, it's absolutely essential that a UASF has extremely strong community and business support, otherwise miners could stay on the majority chain.