Yeah, that sorta already exists. If you've ever done remote customer support, they can send a query to remotely-view your screen -- a query which you have to accept or deny. There's really zero reason there couldn't be a similar feature, but without asking you, and without putting a big red bar a the top of your screen that says "Apple Support is viewing your screen". Wish I had a screenshot or photo of that, can't seem to find a screenshot online unfortunately.