This is a great proposal. This gets over the problem that even if consensus (say 75%) is reached how do we ensure transactions are not lost before everyone (100%) has upgraded or risk being on a losing chain forever.

Under this proposal we no longer need as much as 75%, 55% would probably do and the rest can safely upgrade with all transactions ending up on the winning chain because, by the time we reach 55%, we will know which chain will win.