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.
No it can't. Miner's that signal BU support would currently reject it as invalid.
They designed it with some good features. They signal support of larger blocks but they don't accept larger blocks until either manually turned on or X of last Y blocks are bigger.
proof that if a miner tries blocks over 1mb, WITHOUT consensus... its rejected and trashed in 3 seconds
2017-01-29 06:59:12 Requesting block 000000000000000000cf208f521de0424677f7a87f2f278a1042f38d159565f5
2017-01-29 06:59:15 ERROR: AcceptBlock: bad-blk-length, size limits failed (code 16)
so that debunks everyones scripted FUD rhetoric of how dynamic miners have control..
3 seconds gone.
P.S dynamic implementations need NODE AND POOL CONSENSUS.
segwit are the ones that bypassed NODE consensus. and segwits Bip9 can drop its pool thrshold below 95%. oh and core can UASF ban hammer and change mining algo to get that threshold even lower..
its core with the deadlines and threats..
all while other open and diverse implementations have just run for the last 2 years with no deadlines no ACTUAL threats and just ltting the community have a free open choice.. take it or leave it