While way off-topic for this NUBB board, I LOVE That there is a passionate discussion about soccer here.
I think the the next wave of MLS is starting right now with Omaha Union and my local FC Tucson building a true local tier of the soccer pyramid with their own supporters groups and with players like Tucson's Long and Toia, moving up to MLS. I know promotion and relegation are Euro traditions that the economics of MLS are not prepared for, but I suspect that when USL 2, USL 1, and USL Championship mature, they may move to having some form of it the only questions are will there be space in MLS someday to add teams, it's already slated to be one of the largest (by number of teams) leagues in the world when the current expansions finish.
I wonder about a two league system like the old MLB structure where Eastern and Western Conferences are separate until; the playoffs, or a seasonal system where winter region teams play the current MLS schedule and warmer weather teams play a schedule like the rest of the world.
One last note,Tucson hosts the (Sponsor) Cup every spring and brings multiple MLS clubs and some USL clubs together for days of preseason matches...
"A total of six Visit Tucson Sun Cup matches will be played from April 3 through April 10 at Kino North Stadium, including Major League Soccer (MLS) clubs Colorado Rapids, LA Galaxy, Real Salt Lake, and Sporting Kansas City. This will be the 11th consecutive season that MLS teams will have been hosted and played preseason games in Tucson. The MLS matchups will be streamed on FCtucson.com."
It is a ton of fun to just watch back-to-back-to-back soccer for a week in Tucson in March. (avg March high 75, low 49)