I am assuming based on other prices in the crown store that the houses will cost crowns period.
Guild hall will be 15 to 20k crowns and everything else will work down from there.
Meh. Put it behind the ESO+ and then make all properties and items either craftable or purchaseable for in-game gold.
It's exactly the way it would have worked if the game had stayed sub-only. Sounds good to me.