There's no shortage of failed great technology, unfortunately.
You need a way to get this launched, which means you need widely-available clients (PNaCl), and you need the content as otherwise nobody needs those clients you don't yet have, and you need the tools for developing the content which aren't available, and you need a way to interest enough folks in this technology into adopting it, whether by pushing them (cash) or pulling them (cool, useful, solves my problem, etc).
And you need to sort out and preferably prevent the security attacks and how you're planning on providing content protection (yes, you're going to need some sort of copy protection get more than token commercial content), the usual UI adoption issues for non-tech users (they're the big market, and not the geeks), and with all the usual nasties that can derail or dissuade the early adopters of any technology.
Getting to critical mass with these sorts of products is inherently entertaining, and involves rather more thought and cash and effort than with the technology itself. Have you looked at how all that'll happen here, rather than looking (just) at the (admittedly cool) technology?