I think this is a matter of preference. My main issue with the existing attributes is that the granularity is arbitrary. If Str and Con are separate, why are Dex and Agi not? Personally, I like increased granularity in attributes because, to me, it makes character building more interesting. I can definitely understand the argument for simplicity, though, especially if the granularity is present in other mechanics, so I'm going to work up a 5 attribute system for broader ability scores.I agree with everyone who says the Six Stats are never going to change--they are the sacredest of cows. WotC knows better than to mess with them.
But in the event that Mike Mearls went temporarily insane and did decide to modify the stat lineup... your proposal results in increasing the number of stats from six to nine. That's way too many IMO. Six is already pushing the limit of what's reasonable. I would instead focus on rebalancing the stats better, something like this:
Strength: As written.
Dexterity: No longer affects initiative.
Constitution: Eliminate Con mod to hit points beyond 1st level. Your 1st-level hit points are modified by your Con, but after that you just get your class hit die.
Awareness: All-new stat. Insight, Investigation, and Perception are all based on Awareness, and Awareness determines your initiative modifier. Disbelieving illusions is an Awareness save.
Wisdom: Merges Intelligence and Wisdom into a single stat. No longer affects Insight, Investigation, or Perception.
Charisma: As written.