XPM & Dimecoin are the most potential, innovative and profitable CPU-coins on the market at the moment.
Neither is actually a true cpu-only coin.
I don't think you're getting it. Proof of work is very solid, but other algorithms can be implemented to avoid botnets invasion. Reward for transactions only or other kind of prizes can be delivered. The objective is to not restrict the availability to GPU farms
What algorithm could possibly be implemented that prevents botnets from mining? I think you might be unknowingly heading towards some of the ideas behind pure PoS coins here.
we need a good hybrid coin, PoW and PoS which requires both cpu and gpu to keep away botnets
in this way you don't cut out anybody and any sub-average gamers should be able to join the game.
has this been tried already in the past?
It hasn't because I don't think anyone has thought of a realistic (or even possible) way of doing that. If someone does, I expect it would gain a decent amount of interest.