There is no SQL successor: SQL is here to stay.

Applying the Lindy effect [1]: after half a century of SQL we can expect it to survive for at least as long.

Disruption/displacement of SQL is like attempting to replace email. It's not going to happen. At best an alternative technology can carve out a small niche (and there's nothing wrong with that).

[1]: https://en.wikipedia.org/wiki/Lindy_effect

That wikipedia article was super interesting, I'd never heard of the Lindy Effect before. A bit difficult to wrap my noggin around but really fascinating to think about.