A memached storage engine existed in the past, but I don't think that it is still mantained. It probably has never been mature.
MariaDB 10 doesn't include the Memached Plugin for InnoDB, and probably it wouldn't work if you install it.
So, you don't want to switch back to MySQL? I understand, because MariaDB is more open to the community and MariaDB 10 has more interesting features. But in that case, the only thing you can do is using LevelDB instead of Memcached. LevelDB in my opinion is a good replacement for Memcached. You could also consider the HandlerSocket plugin.
But if you need to use Memcached with transactions or foreign keys, then you can't use MariaDB.
EDIT: I talked about the LevelDB and not Cassandra because LevelDB uses the same basic concepts as Memcached. But yes, you could also use Cassandra (if it makes sense in your use case).