I connected my 3DS to Fiddler as a proxy, but no dice. It seems that Pokemon X/Y (or possibly the 3DS itself) creates an HTTPS tunnel (which is encrypted) when it is set to use a proxy server. I also used Wireshark to capture packets from the 3DS, which also seemed to indicate that the 3DS created an encrypted connection with Nintendo's servers.
I'm not particularly skilled with this kind of stuff, so I don't know if I did things right, but this does not bode well for the possibility of a GTS hack, à la ir-gts. I honestly don't know what the next step is here, or if there even is one.
