I agree. I think it's better if we just create our own individual custom titles, after 500 posts, that is.
But if we do have some sort of ranking system, it should be before the option of creating our own custom title is available. For example, for every 100 posts we make (0-100, 101-200, 201-300, etc.), there could be a certain "rank" shown for our member title. Then once we reach 1000 posts and beyond, we are free to create our OWN member title. This alternative is much less complex than the other suggested ranking system.
It's just an idea though. I don't mind whether you choose to consider it or not.