Further to the feature discussion Enhancing the Prominence & Use of Tag Groups the power of Tag Groups could be enhanced further to include the notion of a hierarchy of tag groups.
This would enable multiple level nesting, as per sub-spaces. This would solve many of the aggregation issues reported e.g. New Feature: Sub-Space roll up under Parent-Space However, this would not apply if there was a genuine need to create sub-spaces for access control reasons.
The functionality for tag group management would likely need to be rationalised and improved. Currently a user can create a tag group, but only if at least one has been created by an administrator. Also the user has no ability to manage tags groups once they have created them. I'd also like an administrative capability to pre-create tags and implicitly the tag groups & tag hierarchy i.e. a taxonomy.
User driven folksonomy's are great, but it might be an appropriate configurable setting to allow this or enforce the use of a provided taxonomy. Opinions I'm sure will vary.