I ended up spending a good chunk of Thursday doing more research on this, despite myself. I looked more deeply into the XMPP (the more technical name for Jabber) publish/subscribe (PubSub) specification. With Jabber server supporting PubSub, I think you could do SIF over Jabber without a dedicated Zone Integration Server. What's more, it seems like PubSub is supported by several server-side implementations. However, as far as I could glean, it is not supported in the existing client libraries, particularly in Python. Yet. At this point, trying to figure out the Jabber specs and existing libraries well enough to do this myself is even less appetizing than returning to my SIF_HTTP code, so I can shelve this idea for six months, but I'll keep an eye on the relevant libraries.