@Zanna If somehow that's off-topic, then the reason is neither apparent nor related to it being of interest to developers. (We list "Development on Ubuntu" explicitly as one of the topics that people can ask about in the help center, after all.)
I think the reason it doesn't is that it's the client-side JavaScript that does (or does not do) tab completion, and the information about all the editors is not provided in any form. Of course this could be remedied by including it, or fetching it when a user comments, or fetching it when a user starts an @ reply while commenting.
I agree. It's of direct relevance to Ubuntu users in a way that it is relevant to basically nobody else, and also we explicitly allow questions about "Services provided by Ubuntu." I don't exactly know what that means anymore, and I'm not sure I ever did, but I can't think of any interpretation at all that would exclude questions about where to find files that are provided officially on the Internet for use on Ubuntu systems.
Most of the close votes are for the EoL reason. I wonder if people didn't understand the question, or were unfamiliar with the technical issues involved?
I think a userscript could accomplish it, too, but if the system changed who gets pinged, the userscript would be far, far worse than useless. If the system changes who gets pinged but @ autocompletion is not updated, then that would be even worse... but SE devs would be able to make both changes at the same time, and if they didn't then there would be heavy practical testing resulting in a bug report and fix, probably in a short time unless only uncommon use cases were affected.
