shower thought: have them been infected now, or now are known to be infected?
This is an important point. This research comes after 10 days of the leak. I have been following the leak closely, I've even compiled a list with all the analysis and resources on a gist.
Good guys, bad guys, kids, bored Blackhats, had enough time to practically follow the step by step instructions in order to implant the backdoor. It doesn't take more than 30-40 mins for the first read till a successful exploit.
The short answer is that we have no idea of knowing how many of those were backdoored by the NSA.
Also worth noting is that the leak happened 3-4 months ago. A lot of people had access to this privately.