i've considered, for whenever i get to run next, a house rule for martials to let them replace attacks with additional types of actions - namely dashing, disengaging, using an object, or escaping a grapple (the last of which my group was effectively already doing since by the time we figured out that was always a full action, we'd decided we didn't care).
that way martials would have not only more mobility, but more flexible mobility. a barbarian can dash 80 feet and cave your skull in with an axe on the same turn. a level 11 fighter can turn away from the guy he's fighting, sprint over to the wizard in trouble, and dropkick the muscle harassing him. a monk can...oh god, a monk can be scary.
i have no idea how it'd actually play...but it's a thought. rogues might need another cunning action to keep up, though.