Given everything.... I reckon it's most likely going to be Kholusia but I think the dwarves will only play a marginal role, or at least not the whole tribe just a few select individuals. Thancred and Urianger are involved in Eden, so it's reasonable to assume the other Scions will be involved in the 5.x non-MSQ content.
Y'shtola is researching ancient Ronka right now which lowkey feels like the perfect way to set up the Trial series, and I reckon Alpinaud being located in Kholusia will hear tell of the Machina Graveyard and investigate it giving us an in to YorHa. Alisaie might join him, or there's a possibility she'll be more involved in the MSQ than the others.
The big Fate Boss from Kholusia to my eyes kinda looks like the dwarves repurposed some Automata tech anyway, so either way I think it's more likely to at least start in Kholusia, then move on from there.
