What if there was a repeatable quest (stay with me!) at each faction's capital city where you could turn in resources gathered from specific points across the world - or gained from holding specific bases (eastern plaguelands style). Entering these small zones would flag you for pvp and you'd either need to be lucky enough that nobody else was there or fight to control these resources.
Once acquired you would hand them back into the questgiver and, based on faction participation that day/week you could set loose a giant war construct that would make its way slowly (and on foot) from a faction outpost towards the opposing faction's capital city to attack a target (think Alterac Valley before it turned into a zerg fest).
You could ride along side this construct, defending it (its aura flagging you for PvP) where as the opposing faction would be alerted to the position and imminent arrival of the war construct via the world defence chat channel.
Protecting or defeating the construct could award tokens that could be handed in for vanity rewards, valor or conquest points.
I realised it's a flawed idea that doesn't really have any leeway for faction imbalances but maybe some sort of phased CRZ or NPC defenders could be added to make up the numbers. It's something I'd like to see at least - a way of bringing people back together in the world to fight against or protect a specific goal.