Hi Peter,
How would a person or exchange decide to accept a payment in BU if it does not know the gate policy of 51% of the miners?
Suppose that the exchange receives B1,S2,S3,S4 (a big block at height 1, and 3 small blocks at height 2, 3 and 4), and an alternate chain A1,A2,A3 (three small blocks). The first is the longest, but the second may be the one 51% of the miners will extend.
Without knowing the policy of at least 51% of the miners (the maximum acceptance depth) it's unclear if the exchange has to obey the longest chain or the chain with higher probability of being extended.
If the maximum acceptance depth of the majority of miners is higher than 6 blocks, accepting a transaction with 6 confirmations is risky.
So BU would set a lower bound on the number of confirmations equal to the maximum acceptance depth of the majority of miners.But miners do not publish their acceptance depth, so basically users are clue-less. I think miners should at least advertise their gate block size and acceptance depth in their coinbase field.