After this, there will probably only ever be one more RWC in a (present-day) T1 country. And I doubt the final one will be in any of these 3 countries - probably Argentina.
So this is a tough question. It doesn't feel like asking the other 2 candidates to be patient and wait their turn - more like telling them they will not be hosting the RWC ever. (again)
I'm probably leaning towards Ireland, but they better do it justice and have the whole country buzzing. In case future RWCs only happen in large spread out countries like Argentina, USA, Russia, Brazil, China.