The When and Filesystem root tags actually use exactly the same frontend code to render themselves: they’re both just hierarchical tags.
This is a great idea! I just added this as a feature (feel free to vote on it): Support different "view by" treatments for tag galleries
Right, this is how it works!
Know that the tags associated to an “asset” are gathered together by “merging” the collective metadata of all the asset file variations: which is why an asset may have more than one folder tag.