I would really like us to have 6 teams. Either a 3v3 or 2v2v2 would be a nice dynamic situation.
An interesting approach might be the opposite of "no razing" -- every captured city must be razed. At least that would mean the winner of a war does not absorb the loser's land and cities, that land must then be resettled. It would be especially interesting in the 2v2v2 if the 3rd alliance is in settlement range of the frontier between the warring alliances. This approach would also generate a "pillage or don't pillage" strategic decision -- if you pillage and then settle the land you removed your own improvements. And if you don't pillage and another team settles there...
An interesting approach might be the opposite of "no razing" -- every captured city must be razed. At least that would mean the winner of a war does not absorb the loser's land and cities, that land must then be resettled. It would be especially interesting in the 2v2v2 if the 3rd alliance is in settlement range of the frontier between the warring alliances. This approach would also generate a "pillage or don't pillage" strategic decision -- if you pillage and then settle the land you removed your own improvements. And if you don't pillage and another team settles there...