Are you thinking about multiple people simultaneously working together to make an item or are you more referring to limiting the number of crafting skills a given player can master so that one person cannot make everything?
If you are talking about the former, there was one discussion about this in the 'Group and Raid Crafting' thread in this forum. There is one problem I see with multi-player crafting: How do you determine who owns the final item that a group crafts?
If you're talking the latter, well, I whole heartedly disagree with limiting what crafting skills a player can master. If I want to master them all I should be able to do so. But, if we find out we can't many people like me will just make alts so we master every skills. Why should I pay someone else's markup when I can do it myself?
Just like different classes will depend on each other, you can expect different professions to depend on each other as well. Probably not quite as much at lower levels, but as you get higher level and craft more complex items, there will some recipes that require items that you cannot make and need to find other means of acquiring them, such as finding another crafter that can make them. That is one reason why you are restricted to one profession per character - to increase player-to-player interaction.