Architect here, who often helps people with kitchens.
"Carousels" are often called "Lazy Susans" here in Leftpondia, fwiw.
Here they come in two flavors:
larger, with 3/4 of a circle, and cabinet fronts on the straight sides. Higher-end ones might have a round liner inside the cabinet to prevent items falling off into the abyss in the back.
smaller, with an angled front of the base cabinet, but with full circular shelves.
I encountered the "magic corner" in the kitchen of some folks who want to add on a garage, and were showing me how the kitchen came out form an earlier project. To my mind, clever, but really only useful for a few pans.
Some times you can access the space under the counter corner from an adjacent room. Perhaps there's a dining room, and you can have a partial-height cabinet opening into the dining room for napkins, etc.
Do be careful to have fillers / scribe strips at the inside corner so that opening a drawer isn't blocked by a drawer pull on the perpendicular side, same can happen with doors. Don't ask how I know this.
Drawers, instead of pull-out shelves behind doors, are good for the base cabinets. If you are having the cabinets built to order, and you know how you (or your parents) stack pots and pans and whatnot in their current cabinets, then you can be specific about getting exactly the minimum clear heights needed. The pull-out shelves, if the cabinets were set up with the 32 mm module, can be adjusted for height (a bit). It is clunkier to open a door in order to pull out a pull-out shelf.