This is one thing that Scott mentioned in his blog post about the Geomodel - eventually using it to surface observations that may be incorrectly identified or represent really interesting finds.
Faving or tagging other users is generally fine, although it obviously depends on the user and the number of times you tag them. You could also make a traditional project for these observations, as adding observations from the Identify page is now possible. An observation of mine was recently added to Undescribed Diptera, for example.
I don’t think we’ll be implementing upvotes or downvotes. Most of the downvoting goals described here can be achieved via the Data Quality Assessment.