- Does it make sense to be an "expert* in kill-count"?
No, because questions with this tag could belong to any fictional universe and you cannot possibly know them all. -1
- Does it make sense for a question to be tagged only with kill-count"?
No, it would need to have a franchise or work tag at a minimum. -1
- Does kill-count have a single, universally-unambiguous meaning?
- Is kill-count likely to be used correctly just based on it's name?
- Are there "enough" (> 15) but not "too many" (> 10% site-wide) questions that qualify for kill-count?
Maybe, there are nine now and I could imagine that a few more might exist but not have the tag (or be asked in the future). >10% site-wide is never going to happen. +1
- Are people like to use kill-count to find questions to answer?
Maybe, some people might like doing the kind of math and trivia this involves. +1
- Are there likely some users (be objective!) who will favorite or ignore kill-count?
Maybe, but I doubt it. +1
- Could kill-count be reasonably used to feed questions to a specialized chat room?
I can't imagine why you'd want to do that, and the question frequency is low enough that there really wouldn't be much point. -1
- Can kill-count be used to search for questions (for any reason) in a way that keyword searching cannot accomplish?
No. These questions all involve one of the words "died," "killed," and "body." You can just keyword search on terms such as those. -1
Final score: +3, which is well into the "terrible" zone:
Very roughly speaking, tags that score > 12 are "good" tags, tags that score < 8 are "terrible" tags, others are likely good but may need some clarification/renaming/etc.
I don't have the rep to mass edit these nine questions without going through approval, but I would suggest that someone with the rep do so, since this looks like a fairly open-and-shut case to me.