Nice!
The main goal of migrating to MariaDB is not performance driven. More so, I think it's in WMF's and the open source communities interest to coalesce around the MariaDB Foundation as the best route to ensuring a truly open and well supported future for mysql derived database technology. Performance gains along the way are icing on the cake.
If it works out, then at some point we should probably tell the MariaDB peeos that they can mention that the WMF uses it. :-)