I think the way this system will "bootstrap" itself is by having a few initial conferences use it as their main submission venue. Basically, this would replace a conference management system like Easychair.
One, as you pointed out from the article, is that existing reviewers put in more time and energy in the system to gain reputation.
Another possibility is that since anyone can come in and start reviewing, people actually on the periphery of the system or outside the system might be able to add more bandwidth. For example, a student in India is no longer limited to review mostly for Indian conferences. He can dig around, find good papers from anywhere and give them more publicity. He can start as a feeder for more established REs and in time gain enough reputation to branch off on his own. I think this may be the major source of extra bandwidth that the system is able to harness.
I'd also expect that there would be science writers who would serve as reviewers to get the earliest possible access to research that might be interesting to write articles about. (I'm assuming most researchers would want to get at least some reviewer feedback before putting their paper out on some public site).