War servers have been proposed (begged for?) since I can remember. People have always enjoyed killing other people. Especially on test servers, so there were many proposals to make a "permanent" test server.
Today, the proposals are more advanced. I myself would love to see leagues (chamionships, as you called them) in Tibia.
We could have short-term, PvP focused leagues/championships. In such leagues, Cipsoft could go all the way and test plenty of ideas and mechanics (even the most crazy ones): e.g. no protection zones, guild wars where you have to protect your guildhall and take over the others, double damage in PvP, old PvP (manual aiming, old dmg/healing formulas, mana fluids, etc), ironman mode, etc, etc.
Then, when the league is finished, participants should receive some cool prizes for their regular characters on "normal" servers. These could be both individual rewards (for best personal achievements - most frags, best frag/death ratio, etc) and rewards for guilds (e.g. for taking over most guildhalls/areas, etc).