The only plausible NSL served on Reddit is for subscriber information related to a national security investigation. Reddit was compelled to provide the records they already had on some username's real name, billing details, and similar---and maybe a list of who they exchanged messages with.
There are a number of English-speaking, self-identifying ISIS members who post regularly in /r/JihadInFocus. /u/thelord4444 is one and /u/AnsarAlKhilafah is another. I wouldn't be the least surprised to find out it was about them.
If I was a national security agency with the ability to perform man in the middle attacks, I'd ask for their keys / certificates and crack encrypted communication, and insert my own targeted payload.
