I'm always in favor of more specific tags. So if the question base is there to warrant a new tag, then by all means add it. I do wonder if it is realy needed at this point (I'm the one, nearly a year ago now, that removed the yafaray tag), Luxrender only has 8 questions, Yafaray has 4, etc.
There are other question groups, with many more questions that are denied the right to get their own tag. Yes iklsr, I'm talking about knife tool
However, I do not think that we should just go and add a new tag for each conceivable render engine, because we have decided to add a "Luxrender" tag. If nobody asks about Povray, then it does not need a tag.
Let the question demand drive what new tags we have, rather then because we decided to create this tag.