Its seems like newer frameworks and languages moves to Postgres.
But where MySQL have always been strong has been in the PHP community. And it still seems to me that there isn't much of a change here. Wordpress is still only thinking about getting Postgres support: https://codex.wordpress.org/Using_Alternative_Databases
Yes, that does seem to be the trend. However, that's all it really is: a trend. Schemaless databases are good for certain tasks, but are also really terrible for other things. It seems that people interested in using new tech like to use as much new tech as possible for the sake of it, rather than because it's actually the right tool for the job.
I know multiple people who have lost literally months of work because they tried to use Mongo in a place where a relational database made a lot more sense (incidentally, they're also using Node), and ultimately had to rebuild and migrate their entire data model layer to Postgres.
That's not a knock on Node or Mongo, just an observation. They're the right tools for some things, and the wrong tools for others. If you're choosing your tech stack based on current trends rather than spending a few minutes thinking what problems you're trying to solve, God help you.
That is a trend. I'm already seeing some startups pulling back into MySQL from Mongo admitting they followed the hype rather than using the best tool for the job.
While it could be the perfect fit for some tasks, I know there are a ton of Mongo deployments that would be better served by Postgres or MySQL.
But where MySQL have always been strong has been in the PHP community. And it still seems to me that there isn't much of a change here. Wordpress is still only thinking about getting Postgres support: https://codex.wordpress.org/Using_Alternative_Databases