redeem scripts with four uncompressed public keys, it's 2020...
I'm guessing that's part of the vanity prefix and not something they're willing to let go unless offered a better solution.
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With that it could even be possible for them to keep their '3BMex' vanity addresses by iterating a leaf of the merkle tree that's used as tweak until they get a Bech32 vanity they like. (Not saying that's a good idea: the privacy and fungibility benefits from Taproot would be gone.)
Clearly you do not care about privacy and fungibility when you are using a vanity prefix. Merklerizing their script candidates is indeed the proper solution.
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combined with output batching
That's debatable. Obviously they sign all their withdrawals in a single daily trip to the cold storage, and we can infer they then broadcast the whole lot in one go. If the idea is to reduce impact on fee estimation and confirmation time, a trickle of transaction throughout the day would achieve this better than batching outputs, which is a bandaid to blasting the mempool with all your withdrawals in one giant broadcast.
