I don't know whether I'd call this a fourth dimension or simple yet another way to look upon the use of tags. Every person will have their own corpus of tags, and those tags and their usage somewhat unique to that person. Taken over time, I can see their perspective on objects based on how they tag them. I wonder if the same could be applied to groups that are tagging objects together.

I say this because Jordan Frank from Traction presented on the same panel, and he showed how some clients have implemented with tags that take on five very specific dimensions. So now the tag end of the triple gets expanded significantly, based on these commonly agreed-upon tags that have additional meaning in the entire group (project status being one of the specific types). With that agreed-upon structure, the group can then conduct operations that are relevant to them around the content and tags.