Rails 4.2 - On The Edge - Which Gems are compatible ?

Is it worth adding a section for Gems that are currently incompatible? and maybe have a link for the 4.2. branch where it is available?

Maybe this could be a section for every new, on the edge version?

So far Bullet and Devise do not work, this is useful information to have upfront, when considering planning to upgrade a Rails Application.

I am happy to start it as I am seeing what works and does not and there are many others who will also see what I do not. And I am creating this list so I know what to watch and when I can consider this as an upgrade option. It might also introduce some momentum for gems to be upgraded