TAGs is very useful and powerful for helping user discovery contents.
I am thinking about 2 new Tag features which may be useful for many use cases:
(1) Category-specific Tags : when user go to a specific category, we can show a set of Tags relevant to that category only (if we have more than 1000 tags , it's not good to show some unrelevant tags for that category).
(2) Tag navigation: for example - we have 2 tags: one is "New York CIty", another is "Sushi", how do we support the use case like this: user click tag "New York CIty" -- it show lots of topics being tagged with "New York City", but the user want to further narrow down to see all posts being tagged as "Sushi" -- but only those topics/posts also being tagged as "New York City". our current tag navigation seems not support this kind of use case yet.
my 2 cents.