* I am hesitant to sign up for yet another source of email without more information about the list membership. Do you already have commitment to participate from experienced CTOs with a public presence (such as Camille Fournier who you cite as inspiration)? That would certainly be an incentive to join. If you can't name names, or if you're bootstrapping and don't yet have names to name, then at least some information about the experience level of folks on the list would help: e.g. "15% of our membership has held a technical leadership or management role for at least 2 years".
* You might consider gathering some demographic information along with email address, for example to help address the point above.
* I'd like to know more about the expected participation model. Your description hints at a Q&A model where people submit questions for open discussion by the list membership, but "mailing list" suggests (to me) more of a broadcast model where the list operators submit curated nuggets of wisdom. As founding members of the community, you'll set the tone; as moderators, even more so.
* As you're building a community, I'd want to see a code of conduct - both to know what to expect from the moderators, and to be sure that people from marginalised demographics would be comfortable participating.
* Related to (and probably covered in) a code of conduct, I'd be more inclined to join a community with an explicit ban on advertising ("15% discount on my product for list members"), recruiting ("my team is hiring an iPhone engineer") and market research ("would your company use this product?"). Not that I have a problem with those things, but I wouldn't currently sign up for something that exposed me to more of them.