Canada

It’s a bit unreasonable to keep parts in stock 50 years after the product was last sold

Depends on the part, of course :)

But realistically, if manufacturers were forced to... say... keep batteries and parts available for 10 years, they may actually start to design their products using more efficient (i.e. same parts), lower waste, and with durability in mind.

It would certainly slow down or stop manufacturers from making proprietary parts for every new model they make.

But having designs public domain sounds like a great idea, and if the right to repair becomes a thing, I would expect schematics to be made available anyway.