If there isn't already one in the game, I'd like to see a reasonably obtainable Atma that increases the rate of magic and melee skillups. Abyssea and Level Sync before it have provided us means to level up quickly, while leaving our various skills behind.
Players have long been looking for a bit of a boost in obtaining skillups. The Martial Master Kupower is nice when it's active, but obviously it's only available for certain areas. It's going to get to the point where those areas may not even be viable for skilling up to the skill cap anymore if it hasn't happened already.