Not sure this would fall under SSPL in any case. It's clear that what Amazon is doing is using Postgres under the hood, not really mongo. So I'm not sure how that would work if you make an interface shim to make postgres look like mongo, are you then subject to the mongo license? the postgres license? the apache 2.0 mongo api license? all of them? what if clauses of them are mutually exclusive? etc etc etc.

Just at a cursory glance it certainly seems like only the apache 2.0 mongo api license would apply. But I guess mongo could try to force the sspl on amazon?