Something like this would be great. I am not yet sure exactly what I would want (not sure about the OP) but would certainly like some way to organize and display tags on the landing page like categories are displayed.
One potential problem is that categories and posts are orthogonal: Auto-populating tags would be nice at first, but could be problematic given that there could be a huge proliferation of tags. Also, there would likely be redundancy as topics appear in different categories.
Perhaps being able to manually add some tags along with the categories could be useful.
The problem I am trying to solve is that I have some tags that I want to display on the landing page, but which span multiple categories. While ultimately these should probably appear in a reorganized category structure, in the interim, I don’t know how to display them on the homepage.
Add a featured topic list to your Discourse homepage. This provides explicit code for adding your own customized topic list to a page. Will likely increase the maintenance burden of the site though since it is not an official solution, and can break on updates.