Let's say the MetaMask provider started to return multiple accounts for eth_accounts. That is to say, where the length of the returned array is currently either 0 or 1, it could also be >1. Would this have any implications for using MetaMask with ethers?
It should work just fine, MetaMask just uses the normal Web3Provider wrapper, which is a simple sub-class around JsonRpcProvider, which fully supports lists of accounts.
Closing this now, but if I misunderstood the question or you have further questions, please feel free to re-open. :)
Oh, I should've closed. I'm perfectly happy, thanks @ricmoo !