> "parallel construction" isn't new. It's also what happens when highly-placed criminal informants help make cases against organized criminals; to use the CI themselves as part of the chain of evidence would be to risk losing that CI.
The difference is that the use of informants to generate investigatory leads is constitutionally unproblematic. There is no constitutional right to not be ratted out by an associate.
On the other hand, there is a constitutional right to the privacy of ones telecommunications. Therefore, using investigatory leads that are the product of illegal surveillance is constitutionally problematic, because of the fruit of the poisonous tree doctrine.
A failure to inform the defendant of how the investigation began deprives him of his ability to argue that the evidence against should be suppressed because it was obtained directly or indirectly as the fruit of an illegal search (wiretap).
https://pay.reddit.com is still included in HTTPS Everywhere ruleset, but as an experimental rule. Navigate to reddit.com, click the HTTPS Everywhere extension icon, and you can manually enable it.
The current SMS-based version of TextSecure uses whitespace tagging for contact discovery.
The next-gen data-based TextSecure protocol (which is currently deployed in CyanogenMod's WhisperPush implementation of TextSecure, but not yet in the Play Store app) uploads a hashed list of the user's contacts to the server for contact discovery.