It would be great to allow @mentions in features. I could see this being useful in:
For me this is a priority because otherwise it's hard to call attention to a feature to someone unless you make them a watcher. But, they may not be be a watcher, they may need to just address one comment. It's pretty important to us, we got spoiled with this using Pivotal Tracker and Trello.
This will be coming soon as part of an updated text editor. We want it too!