Housing and revamp always seemed like a natural fit for me. You wouldnt want to make housing separate from the actual play area of an expansion, and you wouldnt want the house to be stuck in old content in future expansions either.
Proper Housing is a system that needs to work from the getgo, and keep working. And you cannot necessarily move the house into a new continent.
Ideally housing would be placed in an area linked directly to Stormwind/Orgrimmar, and made in such a way that it's always available. Probably by a special Hearthstone.
I did dream of a housing system using the BfA islands though, as that would allow it to link up to any coastal province on Azeroth, which makes it easier to link to future content.
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I imagine the main quest will be Green Dragon based, but transition into Red Dragon as the quest moves beyond the raid and starts setting up the next bit of content.
If I were to guess broad strokes I would say that Vyranoth is the link between the two storylines. She will disappear from the Emerald Dream storyline halfway, and eventually reappear after the raid. Basically the same setup as how Fyrakk was important to getting into Zaralek, but eventually disappeared entirely from that plotline.