No need for a whole new system. You could do this by extending tagger:
- Every thread is required to have one (and only one) of these 6 tags.
- Create a simple filter for tags, similar to the “All Categories” drop-down. Use this to show/hide the tags of your choice.
With more advanced filtering controls, you could even do queries like:
- Show only categories:
DOTA2
,LOL
- Show only tags:
tournaments
,events
And you would get a stream of posts exclusively about those two games, with either of those two tags.