I like it! Agree on keeping things loose and flexible.
Should the salt also be made available in the event so it’s feasible to compute the address and compare it with the emitting contract?
I also wonder if it makes sense to split this proposal into different tracks: stark secret derivation and another account_created event one so it also applies to Ethereum-keys kind of accounts. Probably a third one for contract_address calculation, if it makes sense to squeeze the “ETH_CREATE” opcode idea.