It doesn't necessarily have to be an attack penalty. 5e even offers the perfect tradeoff without having to resort to making you miss more. Bonus Action. You could spend your Bonus Action to add an effect like movement penalty. It would make perfect sense to lose a Bonus Action for taking longer to aim. And Bonus Action would always have a use. It's win-win. Perhaps throw in a Con save to keep it balanced.
Terrible idea IMO.
Now weapons actions = things to always do. The limit is your slot/rest.
With your suggestion weapons actions = things to always do until you'd like to spend your bonus action for something else. Exactly like pommel strike.
Correct me if I'm wrong but most classes doesn't often/always use a bonus action at each turn. If the trade off is a bonus action, most attacks (players and AI) would be done with special effects... And this would be boring.
