As my NFL obsession has waned over the past 3-4 seasons (actually started before Vick, but that year gave it a big push), I have been very into world soccer. It is a very compelling sport and their method of academies, youth development, free agency/team building, relegation and championship formats are very different from anything we are used to in the United States.
I mean it is literally an entirely different structure of "sport franchises" than what we are used to.
So I say this with the utmost respect to both their system (which I am growing to really enjoy watching and following) and our system: The two are not compatible. And I've thought about it a LOT. Written draft blog articles about it. How to create a minor league/development football league. How relegation might work in baseball (which is the sport it would actually apply to best in my opinion).
There are many reasons the "soccer system" works internationally that prohibits it from really working in any U.S. professional sport.
The first thing America would have to get rid of is parity. International soccer (from the German Bundesliga, to the Premier League to the French Ligue 1 to Italian Serie A to Spanish La Liga) does not have parity. Each country's soccer league have top dogs that are light years ahead financially than even the #10 or #12 teams in those leagues. Some leagues might have 5-6 "rich teams", others might only have 2-3. But each, without exception, has them.
Even with some forms of even distribution of revenue it still creates huge discrepancies in team building.
But all that said, soccer is a unique sport where the greatest 11 players can be played very defensively, get a few bad bounces and lose 1-0 or 2-1 to a vastly inferior team. So the "any given Saturday" effect in soccer is very real. In football, that is not true. The best 22 players (and it's really now the best 28-30) will mostly dominate lower level competition. The worst NFL team will likely destroy any college football team (as much as some want to argue otherwise). The way the game is played is too physical that the MOST physical, the STRONGEST, the BEST quarterbacks wouldn't rule the day. It would look a lot like the best college programs facing off against the pansies on their schedules.
The way soccer evolved in Europe from a very "club level", community pub "team" is just different from how our professional NFL franchises evolved (again, baseball's a bit different and might be worth discussion if baseball was played and loved in every community like soccer is in Europe),
I mean just in the little country of England there are something like TEN levels of soccer leagues which equates to something like 200 soccer teams. At the lowest level it literally is a "club sport" of local guys getting paid peanuts to play almost pick-up level soccer games every weekend in 2500 seat arenas (fields). The only way it economically works for these smaller, lesser teams is because England is so small (travel expenses are minimal), soccer is a cheap sport to play (all you need is a decent field and ball and minimal equipment), and there are SO many people that play it world wide that the pool of talent is there not just for England's many teams but all the teams in every other European country (and South American countries and Middle Eastern countries and Asian countries).
Even if you tried to build a 2-league system in America, adding 16 new franchises and playing two 24-team leagues, the new revenue created might not pay for the expense of all those teams. And then you'd have to allow different tiers of salary caps or salary allowances. The division 2 teams wouldn't be able to keep talent vs. division 1 teams and "haves and have-nots" would be created, thus relegating many teams into division 2 status for a generation. Sure, you can hope your team gets a Saudi prince to buy a team, spend millions (or billions) of his own money to buy his way into Division 1 play (this happens in soccer all over the world), but I'm not sure that's what Americans want from their pro sports teams.
The tier system also works in soccer because of the way talent is developed, retained and bought/sold on the open market. One of the most interesting aspects of international soccer is their ability to sign talent at a very early age, something Americans (maybe rightly) sketchy about. Once signed there is very little "freedom of movement" between teams. The most often way a transaction happens is when a team buys a player from another team. This money can be a boon of profit for a small mid-tier franchise in soccer. I mean millions of dollars for one 18 or 19 year old you develope. That type of "transfer money" is what really makes the soccer leagues tick and acts as a distribution of wealth from the rich teams to the mid-level to the poor teams in kind of a trickle-down economy.
With our love of collegiate athletics and the "draft system", I'm not sure any type of relegation system would work. Who gets the first pick of college talent and why would they want to play in division 2 coming out of college and not primetime division 1?
In world-wide soccer there is no draft. Talent scouts sign players as young as 8 years old. Move entire families to their cities and place their precocious children in special soccer/academic schools. Some teams have multiple squads of "under 17" and "under 23" talent that they face off against each other for practice. There a few franchises that have teams in league 1 and also another team in lower tiers that is allowed to advance (relegation wise) only so high. I think Barcelona has its main team and a "B" team that plays in Spain's tier 2 division.
The relegation idea is great in principle but is very hard in practice. And how it evolved in the soccer world is very different from American sports and will (in all likelihood) never really work. Might be fun to think about but the logistics of it, the financial size of American sports, the physical size of the United States in general (and the cost associated with travel) just make the world soccer model unfeasible.