There are some very useful features there, but I can't help but think that MySQL should have had them a long time ago. Is there something MariaDB doesn't have? I'm genuinely curious as I've only really followed PostgreSQL development.
I feel the same way. I've been using and tracking both since the mid to late 90s. I've always wondering why, in a world where PostgreSQL exists, would anyone use MySQL. New releases seems to only slightly close the gap between it and better RDBMSs while retaining quite a few kludges and ambiguities. In the meantime PostgreSQL gets better at the same pace.
I am a solid Postgres guy, but MySQL still has a better multi-master replication story. Confident that Postgres will eventually surpass it, possibly even in a later iteration of 10.
Now in a world where Postgres exists why would anyone use MongoDB is a valid question...