It'll be years before webapps can supplant "native" PC/Mac apps. If Google really wants ChromeOS to be a third PC option, there needs to be a way to run "native" apps, and I'm not sure NaCl is the way to go.
From Wikipedia:
By January 2013, Acer's Chromebook sales were driven by "heavy Internet users with educational institutions", and the platform represented 5-10 percent of the company's U.S. shipments, according to Acer president Jim Wong.