I wonder what it would take? I often have a list or two going, but .txt is just so convenient. Why leave emacs at all?
Current site I'm using is:
Figured a few people might be interested in taking a look at this approach which is different to most others I've tried and quite simple.
Especially since the primary niche I'm building this for is a technically-savvy crowd, such as developers and development teams.
This way you might even use a text file if you prefer for managing to-dos, but Codo would make sure it's synchronized to web and even take care of teamwork-related aspects.