I use Stack Exchange site through my phone (iPhone) way more frequently than I do through the desktop website. When I do that, I really wish that typing the @ symbol would offer the same auto-completion of names that it triggers on the desktop site. Is anyone working on getting that feature working? If not, I'd like to ask that you prioritize it.
There will not ever be plans to implement this on the mobile theme.
We are actively working on the responsive design that works on both desktop and mobile, based on screen size. Once that is finished and perfected, mobile web will be slated for complete removal. While we still fix vital bugs for mobile web, you shouldn't expect any new features to be built for it.