At the time I had another notebook style program named Hog Bay Notebook and then updated and renamed to Mori. Interesting program, but in the end I found myself just using text files on my desk instead of my fancy program. TaskPaper was my attempt at adding minimal organization to those text files.
I remember I got a working program that I used after a day or two. I "think" the first test version that I made public was after a week. The first version was just syntax highlighting, with no model behind it. Version 2 added a model behind it, that took a much longer time to implement.
No agreement other then I made my TaskPaper for iOS code open source and then started with that source when creating TaskMator. I'm happy that they have done so.
Nothing in the foreseeable future. I know I'm in the minority, but I just don't enjoy using iOS devices for "thinking". I use iPad often for watching movies and for playing Carcassonne. Plus there are already 1000's of iOS todo apps, I think my time/effort is better spent on Mac. For iOS my strategy is to make an easily parsed file format so apps like TaskMator and Editorially can exist.
No. It's a wiki page so can be updated. But that part of the website is getting old and I'll likely remove it once TaskPaper 3 is done. This page is a bit more recent: