I think the answer is Datalog. It is simple, simpler than SQL but powerful like Prolog. Why hasn't it caught on?
But yeah, if getting rid of the whole SemWeb stack, triples, and their many awful serialization formats, design-by-committee query and constraint languages (keeping just the good parts) means we can finally return to focus on Prolog, Datalog, and simple term encodings of logic, I'm all for it.
And in the future we will even be able to add constraints - which can be a real superpower in querying graphs.
SQL is not only for queries, it includes a Data Definition Language as part of it I believe. You use SQL to define the schema to which the data in the database must confirm.
Similarly for Prolog and Datalog. You can define the form, the schema of data in a simple way and then the relations between the data by declaring simple inference rules between them.
Datalog has the benefit of being simpler, than Prolog. Simpler is better if that is all we need.
This has nothing to do with http :-)