For anyone that thought the MLS was a flash in the pan it has been announced that by 2010 there will be two more MLS teams. On top of that 7 other cities have expressed interest in having a soccer team. The upcoming Seattle franchise has already sold 3000 tickets, and I don't think the stadium is done yet. MLS rating are either equaling or surpassing NHL ratings this year. I think it is safe to say that professional American soccer is here to stay. Next year it will already have out lasted the NASL. However, lets be realistic about US soccer. The MLS can equal the NHL, but this is still a football and baseball country. It is just soccer will coexist with the other sports.
European professional leagues are also interested in investing in MLS teams.
I believe it is also wise for the MLS to expand in medium to large cities that don't have franchise from the other US sports.