These are just ideas that came to my mind.

1. Split campaigns to hours.
For example my prime time to play PvP is 20:00 22:00. I just want to see same stage of campaign when I start playing next day.
If someone plans to play 4 hours every day then he can play two campaigns.

2. Add softcap and ability to change Alliance at any time
So people from overloaded campaign can easily switch to other if they have problem with waiting in queue.
We need just to tell: Cyrodill is not w WAR it is a GAME. In the war there is one winner who takes over all and then rules. In game there are rules so everyone have always equal chances. In Cyroidill being in more populated side gives you winning automatically - that is clear in real world war, but should be balanced in games (so there are no competitions where winning is assigned to bigger team just because there are more US players then German players).
In 90 days campaign it is usually clear after two weeks who will win at the end, so those who loose have clear demotivator for playing PvP in 70/90 days - I would never plan any game like this to make people demotivated.
So campaigns should also take 2-4 weeks.

3. Remove AoE limits on offensive skills
When offensive skill can be used on max 6 players then group of 30 players running aka bot mode (all in close proximity) will win and there is no other tactic - just bigger group gets less damage and it become the only valid tactic right now. Additionally healers have easy work with such group just spamming with one skill.
If AoE works on all players in area then such group would need quickly to split into more tactical formation because they would be targeted.

4. Reconsider what skills should stack and rebalance classes
Having OP damage class (DK) and OP defense class (DK) and class with best support/cc skills (DK) and giving them OP ultimates that stack is leading to only one tactic for crowd of DK's healed by few templars in PvP.