I think this would be a nice little feature and shouldn't take to long to incorporate. One members uploads it and can list contributors with what they contributed.
Using @UserName saves time over having to manually link to people. I assumed it was a bug that it doesn't work in resources, but I was told it was a deliberate choice.
I think Xenforo should strive to make all of its add-ons work the same as the core for a more consistent user experience. I'd be interested in knowing why Xenforo decided not to implement this for resources.
I think this would be a usefulness addition, particularly if you want to mention someone when posting an updated to a resource and to let them know its available (eg to fix a bug they've reported). I've tagged in an updated and have also been tagged in someone else's update but the tagging and alerts don't work.
@owls8521 make sure you like the first post of a suggestion to show you support the idea, as devs use first posts likes as an indication of popularity.