As a task creator, I would like to have usernames auto-complete (aka typeahead?) inside description fields so that I can reference other users more easily.
There were several solution proposed on this task:
https://secure.phabricator.com/T3725
I think most users would appreciate it live in the remarkup block. However the "insert object reference" solution would be an extremely helpful intermediate option.
This is also tracked in the wikimedia task:
https://phabricator.wikimedia.org/T119230