PKing: yes, Ive always wanted at least some kind of K-D ratio stat. Maybe not total ratio (when you have a lot of kills and deaths, one kill or death isnt going to affect your ratio at all), but maybe a "current ratio" that gives your ratio over the last several days.
"Castling" (Towering): This wasnt necessarily meant to be a PK-based activity. However, your idea is very interesting. It would require much more skill from tower guild members. The problem (aside from the complexity itself) would be arbitrating what the new HPs should be. Youre saying the attackers must kill the defenders "x" times more than the defenders kill the attackers in a 10min timeframe. The difficulty here would vary greatly depending on different towers and the number of members online in each guild.
By War Room, do you mean the big empty place in the spar arena with the secret farm? That place has never had a purpose...
Guild Spar: yes, and yes. (the practice guild spar could be McCormicks basement. no one uses that arena...)