Brillaint. I love "Gods in Spaaaaace!"!
The text at the bottom (about alternative Oerths) was very interesting and made me wish I had seen the conversation at Greytalk.
From a Spelljammer point of view, these "alternative Oerths" would imply "alternative Greyspaces". As the City of Greyhawk might not be so important to the gods in all of these alternative Oerths some of these alternate crystal spheres might be named after the central planet (i.e. "Uerthspace") or even another city on that planet (or one of the other planets). I would assume that the other planets of Greyspace would also have modified names in the alternate versions (i.e. "Udill" instead of "Edill").
The normal Oerth is defined by Spelljammer to be a "groundling world", but on some of the alternate Oerths, Spelljamming might be something that has been embraced and individual alternate Oerths could easily be part of some sort of spacefaring empire. Alternatively, Scro forces might have joined up with native orcs and goblinoids and there could be some planets where these "unhumans" are in control of the alternate Oerth. Unless Gary G restricted the number of alternate Oerths, the possibilities would be endless.
I have seen a MWP Dragonlance RPG book that has an entire chapter about "alternate Krynns" (Legends of the Twins
- Chapter 4), so this concept is not something restricted to Greyhawk. I'm not sure how useful that book would be to Greyhawk fans, but someone who was a fan of both settings could probably draw inspiration from that chapter (and the time travel stuff) without worrying that the rest of the book was less useful to them.
Dragonlance seems to do a single timeline thing (where you can
* change Krynn by going back in time, but that destroys "your" version of the world). This alternate Oerths concept seems to be a bit more like the Science Fiction TV show: Sliders
. I get the impression that travel between alternate Oerths would be rather similar to Planewalking (but without a bunch of planes that have funky laws of nature). I can imagine a "Oerthscape" campaign where some sort of "doorway location" or "reality hopping magic" allows people to visit alternative versions of the places they know and love.
* = Actually some sort of law of nature stops most races from changing time and only races created after that time (kender, gnomes and perhaps dwarves) are able to change the past on Krynn. I wonder if a character from another crystal sphere (like Greyspace) would also be immune to the restrictions on changing the past.
As someone who likes Spelljammer and the ability to jump from one campaign setting to another, I wonder how this would all fit into "the multiverse". Would alternative Oerths actually be located on the same material plane (but placed far away on distant crystal spheres floating far across the Phlogiston? Or would alternative Oerths each have their own multiverse (as well as their own crystal sphere)?
I would be tempted to spin out an entirely new multiverse (inferred from the individual Oerths) and try to create alternate Krynns (and alternate Krynnspaces) and alternate Torils (and alternate Realmspaces) that fit in with the concept that GH has set up. And I would be tempted to make Greyspace the only place where people can "break through the reality barrier" and therefore the centre of any world spanning campaign.
But that is a "big" concept. I look forward to seeing how Gods in Spaaaaace! will tackle this on a "smaller" scale.