Where ZOS could disable or tweak certain abilities that they suspect may be causing or contributing to the lag monster and a place where they could test things like lifting the AoE cap entirely and so on ...
Of course, they would have to heavily incentivize everyone so that some people would actually go there and use that campaign.

The player base could actually experience and provide immediate feedback on what they are working on to try and fix things. That would certainly help moral a lot.

It's probably not that easy to create a test campaign and I'm just dreaming of a better Cyrodiil. I love this game. I love the PvP and I truly want to be playing it for years.