One big worry for the SL is what the long-term plan is for financial growth and sustainability. JP Morgan will given them a large sum for the first few years, and they might get some sponsors or even broadcasters to show their games, but what about after, say, 5 years? How will they grow? What's their plan to prevent financial stagnation?
Honestly, I wouldn't be surprised if they decide to expand the SL and invite more clubs in as members just like MLS already does. In a way, I can see the SL becoming an elaborate Ponzi scheme just like MLS is.