Well that would almost certainly kill bitcoin-XT, (even 75% is stupidly risky, the very idea of forking this way is stupidly risky). but that figure is irrelevant. All that matters is that the currency that Bitcoin-XT uses right now is Bitcoin. Any client could change their currency at anytime if the developers of it decided, electrum, bitcoin core, armory. We don't know, maybe tomorrow electrum could switch to litecoin, who knows its certainly possible but highly unlikely. Much in the same way bitcoin-XT will switch if they hit 75%, its still a maybe it's highly possible they wont. You see what I'm saying? this is the actual censorship that is going on.