Also very unconvinced by the BIPs that either will even work, irrespective of whether they’re good ideas or not
256 sidechain limit is dumb, not nearly enough
Bitcoin nodes should know as little as possible about sidechain, keeping lists and hashrate escrows seems pretty non-ideal
New messages for sidechain proposal and BMM request would surely lead to massive node p2p traffic, swamping the network (how do you know what is and isn’t spam if it’s supposed to be blind? You can’t?)