Interesting idea. But why so many magnets? Wouldn't a few magnets dropped into the countersunk screw holes in the standard plate be sufficient, and way less work?

It'll work ok to begin with but you'll find the magnets loose their "stick" if they're directly in the hot zone over repeated heated builds.

Edited to add: ...but that could have been specific to my own experience where the magnets were also being used to conduct the electricity to power the nichrome wire used to heat those early build platforms.

Great Idea !!!!!