40 man zergs in a cramped environment is boring and destroys any build diversity, because everyone is expected to use the same skills for maximum zerg efficiency. In general very few people are really happy with IC PvP. My suggestion is to make different Imperial City sub-campaigns, and only allow a certain amount of players (like 20 per alliance) in each sub-campaign.
This way you can force small scale PvP, which is the most fun type of PvP, and you eliminate those giant zergs. There will always be players that want to go around alone, or with their friends or with a smaller group, and this way they won't be run over by 40 man zergs. In IC you'd only allow 5 man groups, and disable Trial-size or zerg-size grouping.
If you implement this you can also shelve the tri-alliance arena idea, since this is more or less the same.
Edited by Zsymon on August 5, 2015 12:09PM