Hmm although I don’t think user onboarding should be handled by the RPC, it’s true that someone, whoever is onboarding the user, has the power to influence what account contract will be associated to the user’s keys.
So it makes sense to have an upgradeable proxy associated to a pair of ethereum keys for the reasons stated above, but there’s the problem of some party (e.g. uniswap, coinbase, infura) choosing your account contract for life. I’m buying into forcing that this CREATE method instantiates a proxy, to protect users from tying themselves to a given contract unknowingly.