I will add one other thing.
There are a few tweaks that would help the sport in the U.S.
1. Play on the smaller football gridiron (keeping 13 a side). Many (if not all) of the AMNRL and USARL teams play on existing football fields and the quality of the sport hasn't suffered at all. Yes, you would be using yards instead of meters. If the sport becomes bigger, there are a lot of NFL and college football stadiums that sit quiet during the summer months.
Are the fields scalable to upgrade to the proper size?
It may not matter to amateurs, but 100 metres compared to 100 yards is a big difference to professionals. The distance the defensive line had to stand from the ruck moved from 5 metres to 10 metres for a reason.
2. Slightly alter the uniform. American football got the pants right and rugby league would do well to adopt something similar (without the pads). These pants would make it very difficult to grab and use for tackling. It also prevents seeing a player's bare ass during the game. Many league players wear the biker style shorts under their game shorts anyway.
I don't think it's in the best interests of the game to make legs more slippry to tackle.
3. Possibly tweak the terminology. Touchdown is the more correct term for a try and it makes more sense to a new American viewer. Also, terms like "out-of-bounds" should replace "in-touch" and "try line" & "touch line" with "goal line" and "side line". The main purpose is not to confuse new viewers and make them feel comfortable with the lingo.
Can work easily within the U.S.
There are differences in position names between Australia and England.
Five-eighth <-> stand-off
Lock forward <-> Loose forward
Domestically they have no bearing what you call them.
4. Static Uniform Numbers. Fans need the ability to relate players and numbers. For a sport that has to promote star players, this is important. Wayne Gretzky, Mario Lemieux, Roger Staubach, Joe Montana, Michael Jordan and Larry Bird. You may know them as 99, 66, 12, 16, 23 and 33. Although other leagues swap numbers on players based on positions, it may be more important to to know the players instead.
This was implemented during the Super League break-away era. It didn't gain traction amongst Australian fans. There is something about 'earning' a spot.
When Jonathon Davies switched from Union, the first cultural difference he noticed, more pronounced in Australia albeit, was that their was fierce competition for each position. Reserve grade scrubs would not show him respect due to his name. He understood the increased intensity made for better players.
The fans know this, and there is something to be admired about 'earning' a starting 13 spot.
England I think has static numbers for their jerseys.
5. No more than one sponsor on the jersey. You have to think of jerseys as potential merchandise and no one wants a shirt that's loaded with sponsors. Yes, I realize that sponsors are currently an important revenue source, but I'm looking in to the future when there are more and better revenue sources like ticket sales, merchandise and advertising.
Well in the U.S, it'd be wise to make that a rule early. If they don't currently have sponsors, then you aren't depriving them of any with this rule, and it stays that way.
But yes, please hurry up and get on board.
Qualify as the 4th team in the Four nations, being competitive and host 7 games in packed stadiums in your country, it'd be a treat.