my idea is to use bitcoin core and it's multi-wallet capabilities as the back-end of a mobile wallet app. The way I think this could be archieved is by creating an empty wallet with
bitcoin-cli createwallet true and then using the
importmulti RPC command to upload an output descriptor with an xpub.
Disregarding the privacy issues, the only other thing that worries me about this is that some wallets might cause the node to re-scan the blockchain, and since this can potentially take a while, all other clients will be basically denied their service.
I have not really tested this, but I'm pretty sure this will prevent this architecture from ever working. Am I right? or is there a way around this?