If Apple make made something like this, I may bite.
No idea what the ring would tell me what I don't really know and how in the world I would turn the data into something usable.
but for some people that actually sleep well and want to tweak the quality of their sleep it can be valuable. let me give a few example of such tweaks: altering the time you go to bed, altering the surface you sleep on, reducing the amount of blue light you get, playing with the temperature in the room, not using screens X hours before going to bed, not eating X hours before going to bed. I could go on. The point I'm trying to make is that if you already get enough sleep (or you think you get enough sleep) the ring might help you. yes - the price is ridiculous. but it's not about the price, it's about improving a [very] important aspect of your life.
If you want to be scared shitless into paying attention to your sleep I recommend: "Why We Sleep" by Matthew Walker. Everything from cognitive abilities, fertility, risk of cancer and other diseases can be influenced by poor quality sleep. Sleep, along with eating properly and exercise is a pillar for a good quality life. I believe it's worth making it a priority.