An aluminum bike would need a corresponding affixed ferrous piece to attract the magnet, or vise versa. Just commenting.
A powerful electro-magnet would rock! Hit the switch bike gets sucked up into the rafters....turn switch to Off and bike falls into your awaiting hands or on your head.
My bikes take up space in my garage. When I am organized, they are in a neat compact row. But I'm not very organized. They do get in my way, or one of them gets in the way of another for things like maintenance. My problem is no wall space. I have garage doors in front, windows on each side, and cabinets lining the back wall. In between the windows are wire shelves holding seasonal household items. I hang two kayaks using the rope/pulley/cam locking system intended for bikes.
This system works, gets the kayaks up, out of the way, almost too well....too much of an ordeal if you wanted to take a quick bike ride.
I had thought about a ferris wheel, like they use at Home Depot or Lowes for rolls of carpet.
Your bikes would revolve up, around, and down. at the bottom most position a bike could be held for maintenance, or placed/removed when riding. Want a different bike? Hit the button and it revolves around until the bike you want to select is in the "deployment" position. You let up on the Momentary Switch, and grab that bike.