[petercooper]

It seems to me that the only way to bootstrap something like this is with ad spend or viral social media content that inspires people to subscribe, but that's sort of a chicken and egg problem if you don't already have wide reach.

It's not as chicken and egg as it may seem. Let's say you want to create a newsletter about, oh.. TCP/IP, say. You write some interesting articles about TCP/IP related topics, interview some people in the field, put together some cheat sheets or something.. build up a useful Web site about TCP/IP teasing your newsletter somewhere on each page, submit things from it to Hacker News, Reddit, and relevant places enough, and eventually something will work out.