I suggest we continue the discussion here (i moved the thread to the wallet ring) as the other thread is too generic and has already seen some unrelated discussion.
I do not mean to say that the proposal should not be part of the wallet_ RPC methods though.
As for replying to your comments there :
Using EIP712 might indeed not be desired.
As for a fixed message to be signed everytime, I think this is not a good security practice. Every dapp would then be able to get the signature for every other dapp unless we separate them via origins. I think it is important to let the dapp inject a random payload as a signature challenge.
That is why I was asking how you envision the possibility to add the required random data when using eth_accounts or other such methods.
This could simply be an extra parameters to the eth_accounts, etc but I do not see the issue in being simply a separate method.