Because the WotLK client doesn't support it, perhaps it could be implemented via a script command, say '.warmode on', perhaps with a time or location restriction to switch it on or off. In retail, you can turn it on in any rest area, and off in any main city.
I think this is something that many players would enjoy. It's blizz-like... not just for this expansion. And it's a neat idea anyway. Would you guys like it when leveling? Would you like it as 80s?
I <3 world PvP, but I mean PvP, the kind both parts find it a challenge they can enjoy, no the kind where one is oneshot miserably by a higher level player, and sometimes even camped. So, when ganked, turn off warmode, and go on with your business. When in the mood for some fair PvP, turn it on.
But then again, with adequate time and location restrictions, to prevent certain abuse. Possibly with the same restrictions of retail.
And there'd also be the possibility of bonuses and incentives for turning it on, like in retail.