BLF over multiple Asterisk installations linked by VPN/IAX

Inclined readers,

A customer has tasked us with evaluating a multi-site installation with independent PBXs linked by IAX links (full mesh).
We can pretty much fulfill most of the requirements, but one possible showstopper is that the guys want to use BLF watching extensions from other sites (which means that the phones are registered to another asterisk server).
The sites are linked using IPSec tunnels an will also use local E1 breakouts using Digium TE4XX cards.

From what I have read about distributed device states there either is the openAIS/corosync implementation (which I think will be a major pain in the *** in this environment due to the network infrastructure) or by XMPP PubSub
As the article I have found ( is from 2010, I wanted to ask a few questions:

  1. Is there a newer technology around that does not necessarily require extra servers (Tigase) and technologies just to distribute the device state?
  2. We are talking about approx 15 sites worldwide. Has anyone of you guys implmemented DSS in such ‘width’? What were your experiences?

Thanks in advance and Greetings from Austria