But you could also use SQL for that new RDBMS, or support multiple query languages. It doesn't matter, all relational databases are very similar because they are relational: they do the same things, potentially in the same way, regardless of the query language front end.

Apart from being subjectively displeased at SQL syntax, most problems with SQL are actually query language independent issues in the RDBMS: maddening proprietary extensions, implementation limits, nonportable details, library and system issues (e.g. character encoding and default configurations).

The best alternative query languages can do is making certain queries (advanced, rare ones) easier to express.