Well, if you look at the documentation, this is strictly a fix: no described semantics have changed. I'm ok with the idea of adding an additional ExistenceRequirement::MustContinueExistence which requires that the account continues to exist after the operation, though I don't know if there's any need for it.

This "fix" will now allow the possibility of storage-leaks: an account may now be created (i.e. nonce is written) without an ED balance and therefore that may never be cleaned up. I would be tempted to make the CheckNonce logic aware of this and avoid writing a new nonce value if the account is dead.

UPDATE:
That won't work because there's no way for the system to determine if an account is alive apart from the existence of an AccountNonce, which legally won't exist if it's the first transaction. In short, whether an account should exist is not something that we can handle automatically at a low-level. Runtime practitioners will need to conscious not to allow free transactions from arbitrary accounts that do not aware at least the ED, since each such transaction will result in storage leakage.

CC @gautamdhameja @shawntabrizi and anyone else. Please ensure that this is well documented for version 2.