I am really hoping to get us to Rails 4 earlier rather than later, I would like us upgraded to Rack 1.5 so I can amend the message bus to use the new hijack API if the async api is not there for long polling (hijack is now implemented in unicorn and passenger --pre).
It seems Rack 1.5 is not going to happen in the 3.2 branch https://github.com/rails/rails/pull/9488
I really want to move us to unicorn here so we can run the oobgc. Supporting passenger will ease the install story for many users and make @honglilai happy .
Only side effect is that you can't do connection keep alive with hijack (not a real problem for us as we can handle that in haproxy - in theory)
I had a quick look today and there are a number of gems that are still sort of broken in 4.0rc the biggest problems we have are
acts-as-paranoid has an open PR for support, I can not find anything for
sass-rails is supposed to work but for some reason is not.