I think remote productivity coaching is a great idea. In particular, as an ADHD person, this sort of thing would be an excellent supplement for ADHD coaching. ADHD coaching generally includes productivity checkpointing, but it's considerably less frequent (weekly is common) than what you describe.
I'm not at all sure what I'd pay for this, but I'll throw out there that a good 1:1 ADHD coach is ~$100/hr. I wouldn't pay that for this, to be absolutely clear, since the same level of responsibility as a therapeutic service wouldn't be there and there are things an ADHD coach does that this service would not, but that gives some idea as to value.
Some random thoughts:
* There'd have to be a clear value add demonstrated over a reminder program and more typical self-check procedures like Pomodoro. Accountability is one, I'm not sure it's enough of one. People need to see a vision as to how to make their life better immediately.
* People with major procrastination issues for whatever reason do typically need a lot of handholding at the start to figure out how to organize to get past them. You mention this in your pitch on the site, but I can't emphasize enough that this is where the major value and challenge probably is.
* I'd be very interested in the qualifications of whoever was doing this. A basic outsource PA would probably not be sufficient for what you describe in the sense of adding value past what automated solutions could do. If it were, people would probably just use them for that.
* People who procrastinate also tend to wander off compliance with stuff like this. That may or may not hurt your bottom line (we also forget to cancel subscriptions :) ) but it might speak to the efficacy of your service. How would you address the core problem of keeping people engaged?