One of the biggest problems I've seen w/ siege or pvp is that aggro pretty much means nothing.
What I recommend is for RW to implement an aggro list for siege giving higher aggro generating toons more spots on that list.
I guess, I'm imaging the 2 guilds as 2 big mobs w/ lots of smaller components... the toons.
TAB would cycle through toons that appear in the area and toons that have higher aggro get put in multiple times.
Dunno what the proper breakpoint for adding another spot on the list, but I was thinking this would make Knights very useful in siege. ie, if a Knight is generating 5x the aggro as other toons, they'd have roughly 5x as many spots on the list. So someone using TAB targeting would keep going back to the Knight.
& when a player uses one of those skills where they have the most aggro for 5 secs or whatever, the list is swapped out w/ a singular list; that one player... so TAB targeting for those 5 secs would ONLY point to that one toon. After the 5 secs are up, the original list is put back.