Not agreeing or disagreeing with this as a concept, but I'd imagine that since a number of vendors support arbitrary vlan rewrite on ports that in simple environment you could do some evil things with that. (ie. you could use QinQ "like" ATM Virtual Paths between core switches and then reuse the VLAN tag as a VC). Then, as long as no peer has more than 4096 peers you're sweet. It'd hurt your head and probably never work, but heck, there's a concept to argue about. (Please note: I don't endorse this as an idea).
This would be best managed by a very smart, but very simple piece of software. Just like Facebook or LinkedIn, or what-have-you, a network accepts a "peer/friend" request from another network. Once both sides agree (and only as long as both sides agree) the configuration is pinned up. Either side can pull it down. The configs, up to the hardware limits, would be pretty trivial.. Especially QinQ management for VLANID uniqueness. Not sure how switches handle HOL blocking with QinQ traffic across trunks, but hey... what's the fun of running an IXP without testing some limits? Deepak Jain AiNET