newline handling
Taskwarrior can carry "\n" or "\r" sequences (as long as they're entered with a double-slash) and so translation to real newline characters, and back again, is really up to taskopen. 

Would this be a sed thing? or vim options? or vimscript? 

The end-goal being transparent opening of annotations with \n, that act as normal newlines in the editor, and are reverted to "\n" (or "\r") on saving. 
