On mobile clients, where network connectivity is often intermittent and traffic may be slow and/or expensive, it is important that XMPP connections are optimized so that shared information between a client/server pair is cached on the client and reused in reconnections.
XEP-0305, while being experimental at the time of filing this feature request, rounds up other useful techniques for quick reconnection of an XMPP stream with IM/presence.
I'm filing this bug to track various enhancements affecting reconnection traffic and latency. One already filed is bug #23367 for roster versioning.
XEP-0305 was deferred: http://xmpp.org/extensions/xep-0305.html
Implementation of XEP-0198 (Stream Management)  is being discussed in bug #46700 and seems related.