So I'm modelling my architecture on MartinD's. Easy.
What the whiteboard had was a P2P-ish view of the graph here http://docs.moodle.org/en/Community_hub -- where instead of a clearly hub and spoke model, we have a mesh of nodes trusting each other.
So I am working on a dev plan based a bit on the earlier work we've done with Elgg and trust relations, which had a lot in common with this and yet was strictly centralised. The plan is evolving slowly at http://docs.moodle.org/en/Community_hub_technotes -- though I'd like discussion about it to happen on this forum rather than in the not-very-visible :Talk page there.
It is a bit thick and hard to digest initially, but in short my aim is to allow Moodle installations to identify themselves to each other (not automatically but at admin's request) and be able to pass messages aroun with GPG signing/encryption.
Given that GPG-style sygning and encryption are very flexible, trust relations can be established in a mesh or in a centralised (hub and spoke) layout.
With that infrastructure in place, it will be possible to easily:
* Enable SSO across 2 or more moodle installs, with several options to control it as tight or as open as you want, and reports to visualise who's coming and going.
* Enable cross enrolments across 2 or more moodle installs, with several options to control it and good reports to allow enrolment to cross-listed courses to be paid for under different models.
* Enable some kinds of resource and course content sharing.
And all of this while each Moodle admin has his/her own Moodle under control.
I also want to do this with a minimum of requirements (so far, it'll require that you have a working GPG), and it should allow you to trust any Moodle install you decide to, and still give you good hints that it is safer to trust only Moodle installs that use HTTPS with a proper certificate.
There is a lot more detail in the Wiki page anyway -- I'll let it speak for itself
The Project Plan says I will have a working implementation of this by Oct 31st ... but doesn't mention the year!
Lack of specificity nonwithstanding, this means I will be working on this on top of 1.6, port it to 1.7 once that's released and then merge it into HEAD for the 1.8/2.0 release cycle.
There is at least one good thing here: this is likely to get me into finishing off the multi-auth development work, and clearing out a few other oddities around enrolment and auth. So blocks of work that are useful and ready earlier can perhaps make it into 1.7... if they are any good, of course
Anyway, off to pack for MoodleMootUK. I am posting this to bring a few more eyes, and hoping that there'll be a chance to talk about this with people over there and on the forum.