I like the idea of adding this, but I almost think it might best live in contrib. Thats slightly at odds with the prefix query addition - but I'm not sure that really helps you to integrate the solution generally into the query language anyway - it just reverses the term. I think it might be better to leave that to the user, as its likely to remain a special case anyway. I'd rather even do something like a util reverse method.
So I'll hold out for a wiser opinion, but my initial thought would be to not add to prefixquery, and put the the analyzer in contrib