I really hope so. Football (Soccer) is the best sport evarrrr. Baseball and American Gridiron Football are so boring to me.
It all depends on what the MLS does. If it tries to strangle itself with stupid rules, regulations, restricting teams and salary caps that prevent the talent pool from expanding then yes its growth will be slow.
I can easily see us overtaking hockey in a decade or so. Depends on what kind of tv contract we can get and other necessary reforms in the league.
Baseball is definitely in a decline though to what extent is up for debate. Football is going to have huge problems in the future with health and legal concerns, especially so for all college sports.
Immigration, a more connected world, time, and new talent are all on our side as factors that will promote the growth of the sport.
No one expected what Football would become or ever overcome Baseball. It happened. Never say never.