Not all of them have failed, there's been a successful iOS mobile planner for years (City Char Tracker).
It is not designed to be a clone of Mids at all, it's currently more of a char tracker / database with many
of its own unique features (pics of chars, sorting/searching, emailing builds), but also is a basic build planner.
The OP I could tell in < 5 min had no idea of the scope of work he was talking about, what he was saying
would take years of hard work and testing. I remember seeing the post a while back, and some really poor
UI shots, and time estimate of few months, and knew where that was going. There are many thousands
of unique powers in the game, and with HC that database is still changing. You have to start with some
core features first, and do that well, then add to it later.