This is actually something that’s been ticking away at the back of my head now for years. Having server clusters and instances just didn’t make a whole lot of sense to me: it produces games that are only “massively” from a back-end perspective. If you’re going to do instances, just throw the server cluster concept away entirely. You can scope player names with a Second Life like approach, but then everything else you just instance.
But to avoid that resulting in a mess, a chaotic world of one-time encounters with no chance of community, I’m suggesting a relational index to allow community – or isolation – of the instances that different player characters might see… Virtual shards.