Is it possible to count same playtime from different servers? If someone plays 100 hours on my server1 and than 100 hours on my server2 could he have 200 hours on all of my servers? I don't really know how to change the path to savefile.

I don't think there's really a way to do that without writing something to sync between them.

I would love this feature.  The easiest way would do it is to just provide optional MYSQL support in the plugin.  Both servers would write & read to the same database.