Server support informs me that MySQL will become MariaDB 10.0.
If your support is upgrading entire server DB's, the only question you really need to ask them before going ahead, is whether they are backing up databases prior to upgrading. If they have that, then all is well.
Will this upgrade work on Xenforo?
MariaDB is a drop-in replacement, totally interchangeable.
Should I upgrade to MariaDB 10.0 and why?
You should upgrade to MariaDB 10.1, actually. It has even better performance and stability.
MySQL is lacking behind nowadays, like above, Oracle bought it and now has stalled in relation to database technologies. MariaDB is simply a far more productive DB now, regular builds, updates, security, performance, so forth.
MariaDB is actively maintained -- MySQL is less actively maintained -- Percona is high performance MySQL which aligns with MySQL releases.
MariaDB now contains the high performance aspects that Percona pretty much wrote the book with. If you look at MariaDB vs MySQL benchmarking -- MariaDB kicks MySQL to the curb when using InnoDB tables with buffer pool. And I mean really boots its backside -- 100%+ gains in some benchmarking aspects. Google it to understand.
MariaDB is exactly the same as using MySQL.
My only recommendation is that if you're being upgraded to a DB that now supports full text indexing (being MariaDB 10.0.5 and up), convert any MyiSam tables you have to InnoDB engine type, and uncheck the delayed insert option in ACP options, as that is no longer needed if running all InnoDB -- table locking no longer an issue, as InnoDB locks at row level.
. It only states MySQL: 5.0+
