Something I forgot to mention in my earlier post - FWIW, I don't see any furniture items being completely HHP only. The partition walls and columns could be because they aren't furniture - they look like an addition that would get tacked on via a Nook Phone app or the house customization feature itself. Even if there's items you can only buy in-game via HHP currency, you can probably trade it to others online. It will probably exist in the code for the free update, just not obtainable normally in the base game. That's how they could do it.
Reason I'm guessing this is precedent of NL's WA update - the amiibo items were only obtainable in-game through scanning amiibo, but you could still trade them to others.
I know you could argue that the advantage of DLC-only items is that Nintendo gets money from the DLC, but Nintendo also gets money from online subscriptions. If someone doesn't want to buy the DLC but wants the items, they either have to buy or have an existing online subscription to interact with others to trade for it.