In my honest opinion I believe that the sprite protection was removed because it was making the game die. Gaia was practically dead, and Bodor players were slowly leaving as well.
The consequence of players leaving was PvP was dying too. The only skill that is left is the Sprite Helper which is basically the pot side of Sprite Protection.
The sprite Protection system didn't exactly bring more players to Aeria games. A lot of players quit because it was being removed but instead it bought more players to the game and Aeria Games was still making their profit. Really to be honest, with the Sprite Protection System you really didn't play the game or do any of the work. It did it all for you.
But from what I've heard from others, the Sprite Protection system probably will not return at all. I know others have been saying that the Sprite Protection system should have been added to Quill, but in doing this the Quill server would have slowly died and I don't know about others but I'd rather Grand Fantasia not die.
It may be a challenge to level, but that's now what makes the game more fun. People seem to think its boring without bot, but in fact without it, you make a lot more gold as people want more dungeon runs done. If Bodor and Quill players could make it to level 90 without the Sprite Protection system then I don't see why Gaia players couldn't do it too but as I have stated this is just my opinion.