the 100 mbps is not that much of a problem (you're limited by your ISP)... I think that, with enough users, the CPU, RAM and hard disk space would be shortcoming.
Nevertheless... I think it'd be a great idea to make a website devoted to the creation of R-pi accessories (be it expansion boards, cases, battery packs, etc, etc...). Now that I'm starting to think about it, I'd like to work on that too