[DOOP]Rafal +1
I support idea that each slot must cost some count of XP and will be avaialbe with levels.
For example.
Slot 5 - 400 xp, from level 20.
Slot 6 - 550 xp, from level 23.
Slot 7 - 1000 xp, from level 27.
Slot 8 - 2000 xp, from level 30.
Slot 9 - 4000 xp, from level 33.
etc...
It will protect server from slot spam, will motivate players to be more active and will make game more interesing.