Native Websphere support for Atmosphere not yet
Just a little note that we try to add Websphere native support for Atmosphere. We work really hard to find an API that could allow us to do that, but is simply impossible.
We were able to get in touch with the dev team of Websphere and the dev team of WebSphere Application Server Feature Pack for Web 2.0. They have demo that used bayeux for comet application or JMS to simulate asynchronous connections, but it's not a complete asynchronous solution.
Even with the addon WebSphere Application Server Feature Pack for Web 2.0, you can't suspend and resume a connection. Websphere server doesn't support that. It's not supported in WAS 7.0, but in 8.0 alpha there should be Servlet 3.0 support.
Until IBM do something about that, or wait for WAS 8.0, you will still be able to deploy Atmosphere application on WAS but it will use BlockingIO (one blocking thread by connection).
If that is not enough for you, I suggest Glassfish as alternative. Of course, we will continue to monitor the situation. Maybe the community call could be enough to wakeup them :)
You can follow me on Twitter