Just an idea. Why not? While @Sirrian thinks about next kingdoms and next planes (above Kystara or under Underworld), these factions can be helpful for players. With some good troops, for example. And with total renown increased.
This would need explores in the said kingdoms. Doesn’t it? I suggest 3 isolated kingdoms on Krystara map and when entered there are ways to craft vault troops and/or spend vault keys in The Vault kingdom, ways to craft horsemen in Apocalypse, ways to craft Guardians in the Guardians kingdom. Certain things can be moved out of the currently clustered Soulforge this way.
And then we might have similar “shops” or “kingdoms” in the underworld where we can use chaos shards to craft delve items like treasure troops etc.
I asked Salty on stream about this, she said that it’s not likely. Sorry.