First of all, click on the "Watch Movie" link at the bottom to see what the Folding Text app is capable of: http://www.foldingtext.com.
Folding is part of core ST functionality.
Building fancy todo lists with plugins inside ST is already possible, just look at what Plain Tasks or Sublime Todo Manager can do.
The thing I like most about Folding Text is the timers functionality. Can ST's extension system/Python integration do something like that?