Google Fiber is for the last mile, consumer/business users.

I'm suggesting a non-profit organization or entity that is a holding company for dark fiber assets for tech companies, with a charter that specifically protects the privacy and integrity of the packets that travel over it.

If your packets run over AT&T, you clearly have lost. But if you control physical access, the only way the government is going to gain unlawful access is through someone who has integrated themselves into your org or through an illicit fiber tap. You've significantly reduced your attack surface.

EDIT: You could even go so far as to require different orgs to travel over physically diverse strands, thereby preventing any sort of multi-tenant shenanigans, with the cable being shared ownership.