There might be several ways to do this:
1. Add a tag filter dropdown to the "unanswered" question list.
Actually this could be also useful for many other pages like "all activities", "category pages", "most votes" etc.
Many times users are only interested in a very special tag and want to filter the lists by this tag.
2. Add a dropdown to the tag pages to filter for certain conditions:
- No answers
- More then x answers
- Answers with more than x votings
- Question or answers newer then one month
- Question or answers newer then one year
This filter dropdown could be also added to the normal question or catogery lists.
Which way would be easier to go? Would it be difficult to program a small plugin or extend a plugin like tag-search-pro? Anyone interested in developing such a plugin?