The QueuedThreadPool used in HttpBindManager (which is passed to the Jetty Server instance powering BOSH) uses a hardcoded maximum amount of threads (200).
This number (as well as the minimum amount of threads) should be configurable.
I have re-wired the property used to configure the amount of NIO acceptors to be used for worker threads instead (which is what its name implies). PR in https://github.com/igniterealtime/Openfire/pull/483
Initially, we had this, but Tom changed it (my PR pretty much reverses part of his changes). I've asked him on Github to review, to make sure that we're not loosing anything important.