There are already tags. My thought is that they seem to be trying to solve the same kind of noise issues that Reddit's subreddits solve, except Reddit does a much better job. Having to open up a separate account on each site (linked by one big virtual account) is really messy, in my opinion.
I'd like to see this as well. They could implement a tiered tag system with classification tags and content tags. There are few things as off putting as a smarmy, self-important moderator power tripping by telling me my question belongs elsewhere.