Once SIGINT becomes much harder regardless of their previous attempts to stop it, I suspect that the NSA will become a friend and not an impediment. By that time, of course, the "we have to protect our people" types will be the only ones producing results and getting funding, and the "we have to gather information" types will have long ceased to produce. Thats probably a decade or more off, though.
I doubt this will ever happen. If strong cryptography is ever deployed worldwide ubiquitously, which is a big if, passive ether sniffing becomes much harder, but the SIGINT people will likely switch to active attacks. Defense against active attacks is much more difficult than against passive attacks, and requires a host of technologies besides strong crypto (the one we're lacking most, I think, is a good software engineering methodology). I bet the NSA is doing active research on sniffer viruses and other automated tools for large scale active attacks. Wei Dai