Programmer and Freelancer and fledgling founder here. I share your views about how a todo app is supposed to function. I am actually trying to implement one, now if someone would like to collaborate with me, then that would be great.

I have a simple app called taskit(GPL) that i wrote hoping that it would transition to what you describe, but i didn't really have time for that alone. And it's beginning to show its design deficiencies.