Leaving that Phyrexian discussion aside for a moment, I just wanted to add that I really appreciate the wiggle-room and the open-endedness that are baked into the ten realms of Kaldheim. I think actually fleshing out the ten realms the way they did and really showing all of them in
Kaldheim was necessary to give the setting enough depth and make me want to revisit it in the first place, but knowing that there are probably more than ten realms - as well as some "lost" ones - makes the prospect of returning there even more compelling. It also makes me optimistic that the worldbuilding team deliberately left things vague enough to include new elements on that return while still feeling consistent. A big bummer with
Theros Beyond Death was that the way they handled the plane's cosmology felt completely inconsistent with what we'd been told about it originally, e.g. the way the Underworld works or the fact that a forgotten
goddess of love that existed before Xenagos had been established, and then Creative claimed only one god of each colour-combination could exist at any given time and Klothys had been stuck in the Underworld all along. Not to mention the fact that Calix exists...
Even some of the realms of Kaldheim that we
do know have a lot of ancient history that's only hinted at, e.g. Gnottvold, Karfell and Immersturm (at least when you consider Ethan's explanation for why it's no longer Valla), and I think there's a lot left to explore. There are even some things in the present day that weren't included because they didn't fit the colour combination of the realm in question, e.g. the barbarians of Skybreen on Karfell.
That said,
Kaldheim really makes me long for the good old pre-Mending days when planeswalkers were Magic's gods. I've gone on record saying that the planeswalkers we got in this set as well as the gods are the weakest parts of the world and the set in my opinion, and that really makes me wonder what role Oldwalkers played on Kaldheim back in the day. I've always said I was going to riot if we visited a Norse plane that
didn't worship Fiers and Freyalise, even if they were no longer around (and that it would be a great way to somehow provide an explanation for Freyalise's eye-patch). I like to think that that might have been the case on Kaldheim after all. We know that the current pantheon has been in charge for "centuries", and that the elves used to be Kaldheim's gods before that, but that still leaves a big enough window for Freyalise and other planeswalkers from the Shard to have visited Kaldheim after the Worldspell. Maybe there really was a pantheon of Oldwalkers in charge for a while, before they fell to infighting, or were tricked by the local gods, or something along those lines. I'd love to see an interaction like that.
(I haven't read the final
Kaldheim story about that Elf Commander yet, though, here's hoping that one won't shoot down my wishful thinking...)