Just cut off Dark Elves from being Rogues, grouping them with Trolls + Ogres as a team.
Evil Erudites, Gnomes (lets make them automatically evil for this server), and evil Humans would be another team. They would get Rogues and Bards instead of Shaman and Warriors (cut off for variety purposes), as compared to the first team.
Iksar would be their own team. I'd let them be Clerics and Rangers. Iksar are quite outdoorsy.
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Dwarves, Wood Elves, and High Elves would be another team. They would be cut off from Wizards and Mages.
And then non-evil Erudites, non-evil Humans, Barbarians, and Halflings would be the last team. They would be cut off from Clerics for balance purposes.
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Any kind of team based system, particularly one with different available classes like this, is going to need further modifications to the game. You would have to change things such that certain classes, particularly Clerics, would not being *required* for PvE content. Obviously teams without Clerics should still be weaker defensively and have more trouble with some raids, but that would be the point of a system like this anyway. Each team would have different strengths and weaknesses.
Team #1 - Doesn't have great melee DPS, no trackers
Team #2 - Has no SoW, limited tanking options, and the least centralization
Team #3 - Lacking crowd control and mana buffs, no Ports, but they rule Kunark
Team #4 - Weak caster damage, no feign death, no corpse or player summons
Team #5 - The most offensive ability and mobility, but no Clerics, no corpse summon
I would be looking at Kunark era for this, but with many of the Velious era class changes in the game (particularly for the Hybrid classes) and various other changes to the game world (aka, Kunark content not being so totally dominant over Old World content).