Is there a reason for this other than ifs, buts and maybes?
The performance increases were negligible (with some decreases, as well) so: No reason to switch other than a symbolic statement and to avoid any potential future licencing issues or litigation. The MariaDB project will mirror the free-as-in-beer (and maybe paid?) features of future MySQL versions while aiming to be a "drop-in" replacement. On the other hand, it's better to do it now in case the projects do diverge and the MySQL upgrade path becomes problematic or expensive.