This is supported in smurfy's notifications branch only. Also, I am very reluctant to adding specific app notifications. We can't possibly add support for every single application out there. Also this is against SailfishOS design. We have Conversations interface, which integrates all communications channels - no matter whether it is XMPP, SMS, GTalk, Skype etc. And this conversations interface is already supported by pebbled. I have no idea why some developers chose to not to integrate with this design, instead rolling own solution, that needs to be handled specially.