I've been giving some thought to a set of carhartt farmer johns for riding purposes. In general, I think that overalls might be a good motorcycle pant design. Stick with me, here's what I'm thinking:
Problems with normal pants:
1.) Air leak - winter riders know this one and hate it as much as I do. This is why the crotch gaiter came into existence.
2.) Skin leak - Jacket rides up in a crash exposing skin to cheese-grater pavement. Ouch.
3.) Midsection material bunching - this is where the material of jacket, pants, belt, and layers all interact to create a gut-dig-inning ring of inflexible layered fabric. Having a belly makes this worse.
Problems with one-pieces:
1.) Only good for riding - Want to eat lunch? Want to hang around camp? You're either gonna walk around with the upper body of the suit hanging and knocking people's plates down, or you're gonna have to wear another pair of pants underneath.
2.) GOTTA GO - Oh my god, oh, oh, oh christ why won't this zipper move sonofbitch ugh hurry hurry... you get the idea.
Overalls seems like they'd solve Pants 1 and 2 and mitigate 3 (no belt), as well as eliminate suit 1.
Notionally, I'm thinking if I took a pair of Carhartt overalls and added some hip and knee armor, that'd be a good start. They'd breathe better than leather or textile and could be very easily cleaned. They'd be about as waterproof as mesh, of course, but that's what rain gear is for.
Bonus: blend right in at diners.