It seems this is possible now, to a certain extent. Example on meta:
https://meta.discourse.org/tags/c/feature/docker
https://meta.discourse.org/tags/c/dev/docker
Here on Meta we’ve got Show a dropdown to filter a topic list by tag. turned off, which makes sense for the site in general but results in a somewhat awkward display for a (not-meant-to-be-used-here) URL like this, since you’ll have to look at the recurring category to realise that you’re filtered to not just a specific tag, but a specific category as well.
Here’s an example with that setting turned on:
Also, not that many people would notice, but the URL structure is a bit weird.
Current structure: /tags/c/{categoryName}/{tagName}
Expected structure: /c/{categoryName/tags/{tagName}
(especially makes sense when the view is as on namati.org)
So I’m just here to say it’s cool to see this apparently made it in at some point!
What would be really cool though (because I can never get enough feature love) is if tags could be multi-selected. E.g. I could opt to display all /c/feature topics with the tags planned and v1.5 in them.