The talk was hype to begin with. You can buy a 900 MHz bridge from Ubquiti for $125 (or MicroTik device for $129) and attach it to a Raspberry Pi. How you'd do this is obvious. It's a good DEF CON talk, because it's the application that important, but the technical principles here are extremely basic.
If you look careful at the pic in the Wired story on ProxyHam, it appears they are indeed just using the Ubuiti device. Here is the pic from Wired:
And here is the pic from Ubquiti's website:
I don't know why the talk was canceled. One likely reason is that the stories (such as the one on Wired) sensationalized the thing, so maybe their employer got cold feet. Or maybe the FBI got scared and really did give them an NSL, though that's incredibly implausible. The feds have other ways to encourage people to be silent (I've personally been threatened to cancel a talk), but it wouldn't be an NSL.
Anyway, if DEF CON wants a talk on how to hook up a Raspberry Pi to a UbiQuiTi NanoStation LOCOM9 in order bridge WiFi, I'll happily give that talk. It's just basic TCP/IP configuration, and if you want to get fancy, some VPN configuration for the encryptions. Just give me enough lead time to actually buy the equipment and test it out. Also, if DEF CON wants to actually set this up in order to get long distance WiFi working to other hotels, I'll happily buy a couple units and set them up this way.
Update: Accessing somebody's open-wifi, like at Starbucks, is (probably) not a violation of the CFAA (Computer Fraud and Abuse Act). The act is vague, of course, so almost anything you do on a computer can violate the CFAA if prosectors want to go after you, but at the same time, this sort of access is far from the original intent of the CFAA. Public WiFi at places like Starbucks is public.
This is not a violation of FCC part 97 which forbids ham radios from encryption data. It's operating in the unlicensed ISM bands, so is not covered by ham rules, despite the name "ProxyHam".
Update: An even funner talk, which I've long wanted to do, is to do the same thing with cell phones. Take a cellphone, pull it apart, disconnect the antenna, then connect it to a highly directional antenna pointed at a distant cell tower -- several cells away. You'd then be physically nowhere near where the cell tower thinks you are. I don't know enough about how to block signals in other directions, though -- radio waves are hard.
Update: There are other devices than those I mention: