I don't think it's really needed since it's easy enough to level as it is.
I'd even prefer if it were harder to level, because I myself prefer level 99 to mean something.
But it's a good idea, and it could be useful if it was done properly.
I'd say if it were added after people have made it to 99 that would be fine.
Also making it cost a small amount of gold , no more than 60 would be best.
Just so that everyone can afford to buy them and no one complains.