Facebook API chat client

Since the Facebook Chat XMPP support ends on April 30th 2015, I am currently thinking of an alternative way to access Facebook Chat.

Getting inbox content or receiving a specific message works well using Facebook's Graph API, but to create a working chat client there is need of another two points:

For once, a chat client needs to be able to send chat messages. This should include responding to an existing thread as well as creating new threads (starting a new group conversation etc.).

Then, polling for new messages is ugly. The chat client needs to receive notifications when a new message is being received, similar to GitHub Hooks. A Facebook App may receive some kind of real-time updates, but an on_message_receive event is currently missing.

Some receive_message_notifications permission would also be handy, to be able to use a routing server which sends the message ID to the client via webhooks, without having to grant it mailbox_read access.

Is there something I have overlooked, are there any alternatives not being tagged as deprecated, or is there (currently) no support for an open chat API?