I think the idea is that they would want to lock the coins in place before any fork happens. Your plan seems like it requires the fork to have already happened.
This is not possible without a replay protection, which BU refuses to include
It is possible to lock your coins in escrow before the fork. It isn't possible to do an atomic swap between the Bitcoin chain and an altcoin chain that doesn't exist yet.
Apparently Loaded doesn't want to trust any escrow for 60k BTC.
And you could solve any problem in a decentralized system with a centralized solution (e.g. escrow). It's just not very interesting.