It's almost as if HN could use a tagging system... :)
With features like this, the benefits are obvious while the costs are not. I fear those.
That's not to say that tagging is always a bad idea—far from it. It depends on the system.
What have they been played on historically? Mostly behind the scenes stuff? Maybe I don't pay close enough attention but I haven't noticed much in the way new features/improvements over the past five years or more...(?)
The simplicity you mention is worth a lot, though.