Quite entertaining topic.
First of all, do i believe that the MLS can catch the NHL? No, not by a longshot. Like said previously, MLS is competing with the euro soccer scene wich cant be caught (ill get into this a bit later). Can it gain more popularity in the US/CAN? Yes, soccer is an interesting sport and im sure there are plenty of potential fans in a country with 300 million people.
However i found some comments that i found quite funny. Someome stated that its all about money, im quite sure the MLS can generate enough money to compete with top euro clubs for player salaries, but that isnt enough. The prestige and tradition in euro soccer is just far ahead, just like the NHL is to far ahead for Euro hockey leagues to ever catch up. How many here actually believe that the KHL will ever catch up with or go past the NHL? Someone said that if lets say Messi could earn close to the same amount he does in Barcelona in lets say Indepediente he would sure play there. If Ovechkin would get an offer equal to what he earns in Washington from lets say Dynamo or CSKA would he instantly go there? I think not, there is alot of prestige in the NHL that isnt there in the KHL or any other euro league.
Also, ofcourse you follow your home team in the sport you are intrested in. I am a diehard Djurgårdens IF fan and they have a team in both Ice hockey and football (soccer). So do many other organisations in Sweden. I follow them as close as i can in both sports and cheer for them. However, as i am a huge soccer and hockey fan i also watch the UEFA Champions League alot, even though DIF doesnt play there. I also follow the EPL and the German Bundesliga becuase the level of play is amazing. The very same way i try to catch as many NHL games as i can/have time to (as of late i follow more hockey then soccer).
What it all comes down to is that the MLS wont catch up to the big leagues in europe. Every pro soccer players dream is to play in the UEFA chapions league and i have a hard time seeing that changed to the Champions League in the CONACAF. However i will never say never, but its fact, just like the NHL has been known for the best club hockey in the world for a 100 years the same can be said about soccer, the best club soccer in the world belongs to europe and has for many decades. I am quite sure the day will not come in my lifetime when a soccer fan from sweden says "This weekend ill try to catch a MLS game" opposed to a Serie A/La Liga/EPL/Bundesliga game.
Also i am quite sure that the closed league system will not work for soccer in the long run. Soccer by tradition is played in an open league system. The drafting wont work either, although im quite sure alot of NA talent will be drafted and held in the MLS i dont think a promising propect from any euro country would care if they got drafted by a MLS team.
Just my two cents, i didnt mean to offend anyone just vent my opinions. I wish the MLS all the luck and im sure it can gain popularity, but im sure it cant surpass the NHL for one simple reason. The NHL draws attention from all hockey loving countries because it is the highest level of club hockey. The MLS will most probably never gain even 1/10 of the international attention as the NHL.