Yes, my point is that there must be _some_ people that use email for communicating todos, else your inbox would not have todos in it. Maybe it's not HN readers, but the fact that HN readers actively move todos "out of email" mean that someone put them there in the first place. It's those people to which this product would be targeted.

An email that says "can you pick up some eggs on the way home?" is someone putting "pick up eggs" on your todo list via email. To me, it seems clear that for at least a few people email is a todo system. It's probably so for more people than we imagine.