I hope this example shows why autocomplete would be useful beyond the comfort of the commenter:
I recently had an issue where someone edited a post (which I'm not the author of) only to add one extra line of indentation to a snippet, which made the post less readable and correct. Even though this example is not very urgent the point holds true.
While one peer reviewer noticed and rejected the edit, it still got approved.
I cannot rollback the edit, so I have two options:
- Counteredit: Undo the edit manually by editing. This seems like a very bad practice to me.
- Ping the editor: Ping the editor and ask him to do a rollback.
After trying to ping the editor and realizing that autocomplete does not work (and therefore assuming editors cannot be pinged), I proceeded by flagging the post for moderator attention (first time I used this flag - since it seemed like the only valid option left).
In hindsight this was obviously unnecessary, since editors can be pinged as stated here.
Autocomplete for pinging is a very important feature, because it is the only feedback a commenter gets for whether or not the ping acctually works (and also makes it way easier to ping people with complicated names). So I don't see a reason why this would not be implemented for all pings.
No autocomplete also implies that the ping is going to 'fail'. In case it is intentional to keep users from pinging editors, I see it as very poor security through obscurity. It even pushes users to actions, that are less appropriate (as the example above shows).
Not sure if this is a bug or a feature to be requested. If I am missing something let me know.