League of nations is definitely the end goal there but the thing I'd really like to see is some of these lower tier 2 teams like the USA booking in matches and tours with top level club side - e.g. come do a 2-5 match tour of Australian super sides maybe with an Australia A to cap it off, book in some pre-season fixtures with a top 14 or English premiership side, etc.
Money is an issue with some of these concepts but I don't doubt you'd find teams keen to engage and build partnerships, particularly if you started to look at a bit of player and coach development over the long term. There's so much made of the need for these countries to get more regular exposure to top flight rugby, but the gap to the top of the world is big enough that they need something better to bridge it. The level they're at they would struggle to beat a super side straight off, but would likely compete and gain a fair bit from a few matches in a row, and it's probably better exposure than just playing other nations at a similar level to themselves.
This is probably only tagentially related to the world cup at this point, but if the US do get either 27 or 31 this is the sort of proactive preparation they'll need to engage in to get their team up to speed. Perhaps it's something Australia could help to facilitate, with the aim of shifting them off 27 and more firmly onto 31. I know part of the Australian bid is an offer to include US representatives in the World Cup operations team (assuming they have 2031) to help them prepare off field, so it's not unbelievable they add an on field component.