As you can imagine, pulling data from another apps would take time to implement. Especially because there are so many apps out there. Personally, I'm not sure it would make sense, at least at the moment. Or do you think it would?
The reason I suggest it is that it would give you access to a number of users right off the bat which could be good for getting feedback from a large group of people who are actually going to use your app for their actual to-do list (rather than the informal sort of playing around with it I just did for a few minutes). In the end, it really depends on where you want to go with this.