I'm not sure asking here will get you the answers you need. Talk to lots of people, feel their pain, build an MVP. That said, I'm happy to give my opinion.
In my experience, there are plenty of excellent software tools, on the surface. If you want to innovate, I think you might want to think broader -- about how GTD systems actually succeed or fail.
If you were to ask me about the weakest links in GTD software, it has less to do with the "core" software and more to do with behavior. Challenges I've seen include: (a) Forming the habit to use a new GTD tool; (b) Continuing to use it even when life gets in the way and you revert to another system (such as using email, ug); (c) Making it appealing to return to after a break, knowing that there will left-over cruft in there.
Many successful entrepreneurs started by inventing a new to-do list. This is because it is the only way to come to terms with what it means to get things done at all.
There is literally no better use of a first-time entrepreneur's time than reinventing to-dos.
And as a result "We have reached the todo list app event horizon, where it actually takes longer to evaluate all the existing todo list apps than it does to write your own todo list app."
First time developer? Maybe.
First time entrepreneur? Seems like a recipe for failure. I would have thought it is better to pick a (non-IT) niche that one has a deep domain knowledge in and have a go there.
Well, no, not really :) But I am sure you would benefit from creating a quick one-off system for yourself.
If for no other other reason than due to the sheer absurdity of the idea of procrastinating over creating a to-do list. It's something you can't help but do immediately, and is "self-hosting"!
I might have been exaggerating, but I think it's a good exercise in coming to terms with your abilities and task management ideas in general, to create your own to-do system ahead of anything else you're doing.
In my experience, there are plenty of excellent software tools, on the surface. If you want to innovate, I think you might want to think broader -- about how GTD systems actually succeed or fail.
If you were to ask me about the weakest links in GTD software, it has less to do with the "core" software and more to do with behavior. Challenges I've seen include: (a) Forming the habit to use a new GTD tool; (b) Continuing to use it even when life gets in the way and you revert to another system (such as using email, ug); (c) Making it appealing to return to after a break, knowing that there will left-over cruft in there.