For starters, I think the best way to go about it is to have a delve-like location in a major faction hub or location, where everyone’s personal home is at. You can then get people into your home by inviting them into a party or a raid group.
Ideally I’d like some plot of land around it, but I’m not totally against an interior instance either.
I’ll say a realistic idea here instead of ideal: I think the realistic is that they give us a few archetypes of homes to choose from (e.g a warm cottage-like home, gloomy bat-cave, a wizard’s tower). Inside the said homes there would be nodes that you can swap out and edit to your heart’s content, but for example chairs will always be around the table node you select in a pre-set way, or a fireplace or w/e.
Party invite or raid invite to begin with. Though, if they want to go big with it from the get-go, they could make it so that all player houses are saved in cloud, and then you can create essentially private instances (think of neverwinter nights) behind either a password or invite-only basis.
This could help to create taverns and hub-player houses for all to RP in. Hell, Blizzard could even make a few houses of their own, where people could meet and greet.
The way how you’d get into these instances could be through a separate queue system, or an NPC before your estate from where you can select an instance you want to go into, including favourites or official houses etc.
Some may think that I am very limited in the way how I wish the system to start with, but I see it as a positive: This is a completely new system, with implications that go well beyond just what players want- We also need to consider what they need, and the two are not always the same.
By starting slow and experimental, Blizzard and we will be able to probe what things work, what do not, how to build the system going into the future and keep adding into it. Think of glyphs back when they were first introduced all the way to WoD, or indeed flying.
Edit: However, the MOST IMPORTANT THING HERE IS THIS:
DO. NOT. TIE. PLAYER. POWER. TO. PLAYER. HOUSING.
Blizzard, you can ignore all the rest of my post, but please do not ignore the above.
It should be nothing else but a cosmetic time sink that you want to be in just because you want to be there, not because of x gameplay mechanic.