i'd like to think the people suggesting this is a 'test-run' for instanced houses are right, but I've got a nasty feeling that the devs are hoping this will be an acceptable substitute.

They are putting features into the Island Sanctuary that people have asked for in housing: minions roaming free, gardening with a one click waters everything mechanism, gathering etc..
My feeling is that having given us all these things we asked for, but in a completely different context, they're going to be very surprised when the demand for houses remains high and people continue to complain about the shortage.

Of course I could be wrong about that, maybe they are testing for instanced houses or maybe people will feel the Sanctuary is a good enough substitute for a house and the pressure on the wards will ease, though I very much doubt it.