Actually, it already exists. They are called "tag badges". For instance, two days ago I was awarded the gold tag badge for engine, which means I have accumulated 1000 upvotes (not points) in questions which have the engine tag associated with it. I have had to answer at least 200 questions in order to qualify for the badge. There are two other badges which are earned along the same line, which are the bronze (100 upvotes/20 answers), and silver (400 upvotes/80 answers).
If you as an answerer want to figure out who might have specific knowledge, there are two primary ways you might be able to suss this out.
First, you can find someone with a lot of experience in a certain badge by looking up who was awarded the badge for a given tag. You'd need to look in the bronze category, as there are only two silver badges awarded, and only one gold (at the time of this writ).
Second, stick around and see who answers what. If there is a motorcycle question, the first person I turn to is DucatiKiller. He was an MC mechanic for many years and has a great appreciation for them. If there's a body question, I will send a nod to Jonathan Musso, who has great skills in that arena. I consider myself a generalist. I know quite a bit about a lot of different subjects, but don't consider myself an expert in any one area. I have a knack for asking the right questions of people who don't know much about cars to get the information needed to help them figure out what's going on. Don't get me wrong, I've done a lot of wrenching. You can usually ask me a question and I'll have some sort of answer for it or I can hunt it down on the Interwebz (my GoogleFu is strong!). The only way you would know any of this is if you stick around and get to know some of the guys on here ... I use "guys" in a generic sense. We have a few gals which frequent as well ... this is not a "good ole boys" thing, lol!
I hope this helps you out a little bit and actually gives you what you are looking for. If not, please clarify what you're asking and I'll see if I have an answer for you.