I have always played with CBP, CEP and its predecessors, so I have always played without custom civs as I thought they might break the balance, but I will definetely try some of them soon, if they work with CBP.
Some of them are still functioning pretty weirdly, UUs that aren't scaled up to CPPlevel and some abilities that doesn't seem to work.
I think there is one civ that got a decision that gives you the entire liberty-tree(requiring renaissance era and a huge pile of gold), honestly a pretty sweet decision, made stronger by CPPs libertybuff and by the fact that the free liberty-tree counts for a point for ideology unlock
All on all the more people that actually test them out the easier it will be to gather information for JFD so he can make adjustments.