You got it wrong, we should watch the hashpower and not the nodes:
https://coin.dance/blocksSegWit need 95% signalling while BU is the one that needs 75%.
That's already slightly wrong, BU have already stated they will use 51% if they feel they need to.
And Segwit activation is probably going to change too. It will just activate, period, between October 1st and November 15th, according to the new BIP149
October 1st is a long time away. Hope we don't have a fork before that just because people are impatient. BU activation at 51% could happen because of some rogue miner who produces a block of over 1 MB, I don't think that is BU's strategy.