This is an idea I had last year. The api would be integrated into a wallet and enable resource providers to cosign transactions for individuals. For example instead of just relying on the free transactions from the Greymass team maybe EOS Nation or any other providers could also provide free resources.
Additionally there would be a market for paid transactions, some providers may change less for CPU than another provider, or a provider may give you discounted resources in exchange for following their Twitter account or joining their email list.
When I wrote this idea I got some good interest but there was some indication that Greymass would build this functionality. I’m not sure if there is still any plans for them to add this functionality, but in any case, it would be a great feature to have and not that difficult to build.