I think one of the biggest things that could be done to improve Plo (and I mentioned it in the Cody feedback thread) is to give him the clone tag that he may benefit from Echos passive heal potential, Fives assist call, and the full TM gain from his third ability (not just half and only once it's omega).
But, my thoughts on quality of life improvements. I'm all for a taunt on his second ability, especially since it does piddly damage. Two turns might be excessive especially how slow out the box PK is. Additionally improve the base chance of the debuff to 85%.
More damage on his basic attack (at least 2X). Presently he is out damaged by Echo's by the book assist.
I think the combination of these three things will put Plo Koon in a good place.