Thanks a ton, Lluis!
You allude to one of the main humps we have to work through in the community. Everyone realizes that activities like this are important, and want to contribute, but it’s like trying to figure out how to take the first bite of an elephant.
Putting that aside for a second, the immediate task is to demonstrate OpenMRS working operationally on top of MariaDB. At one point, I played around with this, and got it a big part of the way there, but it failed during the installation process. I think some of the SQL scripts that we use to inject demo data might be MySQL syntax specific.
So, if you wanted to get started… simply trying to install OpenMRS, swapping out MariaDB for MySQL, and help us troubleshoot the issues that might (or might not) come up. Once we get through that step, it seems like getting consensus on what a testing strategy for MariaDB (or any database technology) would look like, in order for us to feel comfortable putting that out in the wild.
Of course, there would be some opportunities to wire MariaDB into the continuous build processes as well that create a “release” for general consumption.
I think given the direction that MySQL is heading, we probably want to move away from it being the bundled package at some point.
I’m sure @burke and @darius will correct some of what I’ve said. 
I think the main thing that this task is missing is someone willing to “own” it and wake up thinking about it from time to time until we get it resolved/wrapped up.
I for one will commit to working alongside you until we get there.