Users code could block Play threads, in practice, this is never an issue, since 99.99% of actions look like this:

    def index = Action { ... }

That code doesn't block, it just creates a new Action and returns immediately.  Most users aren't even aware that you could do anything different to this, only an advanced user would do anything else, and an advanced user should know what they are doing.  I think running the action method in a separate thread is being overly protective of users, and one of the big problems we are having with performance is the number of context switches.  I think this one was just unnecessary, which is why we removed it.