I found How can I find the House of Curios? but it appears that changing what quest you're on no longer matters for starting a game instance. Do you always start in town now?
Is there a consensus on whether finding the Scavenger's Den and Lost Mine rule out having a House of Curios on that map?
That question was likely answered before the Reaper of Souls expansion was released.
Once you have finished Act V, most people play in Adventure mode. You don't have any of the story quests active in Adventure mode. Instead there are 5 bounties in each Act and you can run Nephalam Rifts and Greater Rifts.
I don't know if the spawn rules for the House of Curious have changed in Reaper of Souls, but if I had to guess they haven't. Assuming they haven't, you can still look for the clues in the original question. The only difference is that (assuming you are in Adventure mode) you'll need to exit the game back to the title screen and start a new game to get a new instance.
It can be slightly easier to check for the existence of Scavenger's Den and the Lost Mine in adventure mode. IIRC both can have bounties in them, so instead of clearing the entire zone you can open your map from town and check if there are bounties for either of those locations. If not, create a new game. If there are, explore the zone and see if the House of Curious spawned in your instance.
