Really, I'm at a bit of a loss as to why they switched, but congrats and good luck. Glad to see another MariaDB mention. Just found Galera myself. Wish WordPress supported Postgres.
Makes sense. I guess I've always assumed that while MySQL has gotchas, so too would database X. They come with the territory of databases, being such a large part of any app, yet separate from it and usually infinitely more complex than the apps that use them. To that end, I think it's why some people end up writing their own simpler data stores or caching middleware between databases/OLAP and front-ends. Such written-from-scratch solutions can be easier to debug when things are mission-critical.
From what I've seen with databases, the really complicated part is "setting them up correctly". If you start out with most defaults, something will eventually become a gotcha forcing a schema rewrite or a database transplant using an SQL dump. But that's just been my experience: with databases, expect to not get it 100% right the first time (unless it's not your first time with the technology, of course). And from that perspective, the technology used is less important, it will equally have "gotchas".
That all said, I too will be playing around more with Postgres to see how it compares to the InnoDB/XtraDB I've a hate/love relationship with. ;)
Kind of a moot point since they were using MariaDB anyway, but the MySQL geospatial functionality hasn't gotten much attention in a long time. I remember quite distinctly hearing at the MySQL BoF at OSCON 2011 that the original author of the MySQL geospatial stuff was gone from Oracle. I find it hard to believe that they haven't picked up anyone to continue development on that but when you compare features with PostGIS, there's almost no point in even trying to compete.
/geo-rant