I think there is something more than just a society of assassins. That seems entirely too simple for an entire culture to hold hired killers in such high regard. There has to be a deeper role that they play in the culture and history of Bravos.
I wonder if Jon will be invited to Sansa’s wedding. We know that Jon’s uncle was allowed to visit Winterfell, at least for important occasions.
He is her brother and as the leader of the Night’s Watch, wouldn’t he be expected to have sot of dealings with the Warden of the North. In the first season we were told that Ned had some sort of oversight of the wall although I’m not sure if it was anything more then executing deserters.