The keys are smaller in size than the original payloads but still have to be stored privately and backed up, so the backup problem is not solved.
The best solution of the backup problem is imho multisig.
Sorry if this was addressed previously, but if the backup is a problem (and I believe it
is actually), why won't the wallet create a backup automatically after each transaction, and save it to separate designated place (on the same device as a first step). What I am missing here?