I actually think it would be better for US soccer as a whole if a lower-division club got the spot. It's a better story, so there might be more publicity, and MLS sides might take it more seriously in the future. Plus I'm a sucker for any development that makes it seem like we in the States have something approaching an organic soccer "pyramid", and not just a cabal of rich dudes running a plastic, closed top division.
The one downside is that it might bankrupt a lower division team. The travel costs would be brutal, even if they are subsidized by CONCACAF. The Richmond Kickers dropped from the second division to the third division at one point because….they made the playoffs. The extra travel of the playoffs was too much of a financial strain, so they had to move down to stay solvent (the third division was a de facto regional east coast league at the time).
Countries in Europe developed organic pyramids because there were more clubs willing and capable of playing in the top division than there were places in the division. In the US, this still hasn’t come to pass. The clubs in the NASL and USL are mostly a labor of love. They are shoestring operations that play in small, simple stadiums without much financial support. The vast majority of owners would not be able to survive financially if they had to step up to MLS. Those who do have money behind them have mostly joined the league already: Seattle, Vancouver, Portland, and Montreal. (And some of those ownership groups needed to add investors, such as Paul Allen.)
MLS will eventually face an interesting issue. The league could expand to the size of other American leagues and include 28-32 teams. The problem is that MLS is competing on a global scale and diluting talent that way has harsher consequences than it does in the NFL or in MLB, where there is no international competition whatsoever. I think MLS will be hard-pressed to go beyond 24 teams and even that is a very big number. What happens then? If the league is truly closed – no more expansion – there should be an increased investment in lower division clubs because there would no longer be any reason to hold out for a place in MLS. Even now, a second-division type city like San Antonio has a fairly ambitious D2 team that is drawing upwards of 8,000 people in its inaugural season and has stadium plans.
If an integrated pyramid ever comes to the US – and there are plenty of good reasons to think it never will – it will follow the J.League model. This would mean that MLS eventually would form a second division under the MLS umbrella, populated with a few expansion teams and hand-picked successful minor league teams that meet stadium and financial requirements.
It’s a real stretch, though. MLS’s current ownership has sunk a lot of money into the league and into their clubs and they’ll hardly be interested in a system that could see their investment slide into second division status. That being said, a lot can happen in 20-30 years. If we get to the point where second division soccer has a somewhat significant following, it means that soccer will have grown extensively in this country and profits for all will have risen. Furthermore, there will always be a desire for a national footprint, something that it is difficult to achieve with three teams in Canada and several markets with multiple teams (LA and possibly NYC). If the league stops at 22 teams with two in New York, that would only be 17 US markets. I also think that there will always be fan support for such a system, for whatever little that may be worth, especially if we are at a point where an integrated pyramid actually seems attainable.
If somehow it all worked out, I would hope that the powers that be manage the finances of the system very carefully. The European system is rotten right now and I’d hate to replicate the massive imbalance in revenue that is found between CL and non-CL clubs and between first and second division clubs. There will always be an imbalance, but I want a system where a well-managed club has more social mobility than simply dreaming of a mid-table finish.