just want to provide the PSBT and the private key as an input to sign the transaction...
You mean a
signrawtransactionwithkey type RPC call for psbt ? I guess, we don't have any for now. walletprocesspsbt is the only way, unfortunately.
Yes exactly, it would be very useful for offline signature of PSBTs. Is there any plan to add such functionality? I am right that as opposed to an unsigned raw transaction, a PSBT contains all the required information to sign it offline (excluding the private key)? Thanks!