...would there be more limits on this and other national team tournaments imposed by clubs? And would that hinder the growth of soccer at the international level? This premise is, of course, most valid if the World Cup was not essential to the growth of club soccer and the prominence club soccer enjoys today. I'm not an expert on telling when the World Cup really became a big thing, but say the inaugural World Cup was pushed back thirty years. Or more so, when the television furthers the idea of a global setting accessible to everyone. Would clubs have more of an influence on the national federations if demand for national teams was fostered late? Consider that the ongoing World Baseball Classic is touted as one of the highest level tournaments in that sport, but it is in its infancy. MLB teams have been able to place limits on the national teams in using pitchers. Clubs in soccer would be hard-pressed to wage a similar fight and earn similar results regarding World Cup play, but only because it is the premier tournament in international sports, and that is primarily because of the history it enjoys. Had it less of a history, I imagine it would be more difficult for the World Cup today to increase in prominence at the rate it did.
This last paragraph is undoubtably true. Think about it, the World Cup is glittered in prestige, the most recognisable and most watched event in the world. It has so much history, so much drama and so much pulling power that if a club told a national federation how much a player could play, the player would never listen to the club, nor would the federation. You have identified the Baseball Classic as a high level tournament in its infancy. Not knowing baseball all that well i can understand why the MLB clubs have restrictions, because ulitmately, noone really cares that much about 'World Baseball', and as far as i see this tournament, it will never amount to anything like the World Cup. If you swap them around, the World Cup with the Baseball classic, and when they started, it would be exactly the same! Maybe if that had happened, Baseball may be the 'world game', and the World Cup could be seen as a money making scheme, or just some stupid mickey mouse tournament in the offseason just to entertain a few people just for the sake of boasting your countries pedigree in that chosen sport, where clubs can choose whether to send their players to the tournament. Its an interesting view that you have put forward, its made me think very hard! Probably the hardest in a few weeks!
I think you have to factor in the fact that the Olympics would be running on an older, parallel track, and would have filled this vacuum to find a "World Champion." Perhaps without the World Cup, the movement to bring pros into the Olympics may have come much faster; I suspect there would have been some kind of age limit to allow players playing on pro teams to particpate, and thus creating the club vs country issues we have today. I think think the Olympics probably could have grown the game just as good, and may have even pushed the movement faster/bigger if there were no World Cup.