Personally, I do think you can have a decent stab at predicting where a country will be in 10 years time. Most of the players who'd be involved are a decent way through the system, if not actually playing. I can tell you whispers of who to look out for in England U18, and I bet people here can tell me the same about their countries. You hear whispers of who's got strong age groups coming, who's academy is improving and so on. Maybe not as fine as guessing who'll be number 2, but you know who will be within the ballpark and who won't be. I've seen people using Wales being a third seed for the World Cup being an example that you can't tell; I think everyone at the time knew that was a blip that would look somewhat silly/cool near the time.
Anyway, to turn on my tail for a moment, here's what the US do have going for them -
An increasingly strong pool of European teams desperate for talent.
*** Lamositele is the standard bearer for this. He's a tighthead prop, he's only 20 years old and Saracens have already given him a pro debut. I don't know whether he'll make it there, but he is getting as good a rugby education as he can ask for. His chances of making it somewhere are as good as just about anyone in the rugby world.
Cam Dolan will also do the US good as well I reckon. Got a contract from Northampton at 23, might not have played much for them but he's done well enough to get a contract with Cardiff. Scott LaValla did time in the AIL and with Ulster Ravens and is now doing well with Stade Francais.
And so on. When clubs like Bayonne, Biarritz, Lyon, Perpignan, Bristol, and Yorkshire, have players like Adam Whitelock, Ngwenya, Bonnaire, Nalaga, Porical, Henry Tuilagi, Marty, Evans, Henson, Peel, and Walker, you know there's an incredible squeeze on resources. Pro rugby needs more resources.
Rotherham have six players taken from the Irish academy system. Virtually every French club has a Georgian prop and a Fijian wing. If US colleges can produce a sufficient level of talent, then visa issues aside, they'll be welcomed with open arms - and if they show they're good enough younger, they'll be taken younger. If someone points out the next Samu Manoa out to Saracens aged 16, then Saracens will try and sign him and get him a scholarship at one of England's big rugby schools.
The USA can be the next Argentina; a decent international side that competes well on the back of a decent domestic system feeding players into Europe. Maybe the US could look into entering a team into the Currie Cup, maybe in conjunction with Canada if they had to. Is the tap on full enough blast to really create a team capable of beating Scotland and Italy (assuming they stay stable) in say ten years? I'm not sure on that one, but the flow will only increase.
And, while there are problems with exporting all your best into the maw of European club rugby, the fantastic thing is doesn't cost the US a dollar beyond what they're doing already. And to increase what they're doing, all they need to do is invest in youth rugby, which they're already doing.
I do believe that's their best route to success. 7s will drag away players as well as create them, players qualifying on residency will spend 3 years playing a level of rugby too far below the standard required (assuming they don't increase it) and a pro league capable of producing good enough players will take a lot of time. The colleges will be their actual pro league and it will feed Europe until such time rugby seems a good enough business case for America to sit at the table.
And that is when the world will change. But I give that 15 years or so minimum, probably more like 20, maybe more - and the rest of the world will keep marching forwards to make that harder in the meantime.
p.s. Seriously, I think the 7s thing is overrated. Look at Isles: he took up rugby at 23. He gains a pro contract aged 24, but gets nowhere as he's still learning the game, then returns to 7s to concentrate on the 2016 Olympics, which is why people take up 7s. He might return to pro rugby aged 26/27 - lets say it takes him a year to learn the game to full standard - so from 27/28 he's an option for the US rugby team, only he returns to 7s again for another Olympics post World Cup. The US 15s side get really very little out of that.
Others will do better, but I wouldn't be surprised if that was the basic experience of most guys the US attracts to play 7s.