In an interview Sony gave to AV Watch recently, the company admitted it's going to "gradually end development and production" of recordable Blu-rays and other optical disc...
Don't fret, Verbatim will still be making recordable BD-Rs. However, this will mean that there will be no more 128GB BD-Rs, we'll be stuck with only 100GB BD-Rs (Sony is the only company that makes 128GB Blu-rays).
I recently ordered a pack of 128GBs from Japan. I'd recommend you do the same, because the prices are gonna skyrocket.
Backing up personal data, mostly stuff from my childhood that is irreplacable. Sure, I could just put them on a HDD, but then I'd have to replace it every 5-10 years. Data stored on Blu-ray can last a long time.
Rated for, but that doesn't mean they're all actually manufactured to that standard.
CDs were rated for like 50+ years originally I think. We found out real quick that was an optimistic number, especially when you buy the cheapest thing around.
The international organization for standardization has rated them for archival use in the hundreds of years. This is not a maybe and the Wikipedia page/link I shared above goes over the testing methodology
ISO certification does require a bit more effort than just the bare minimum necessary to legally advertise specific claims about a product.
That doesn't mean all M-Disc manufacturing is immune to shitty business practices of a manufacturer, but they do have to meet certain manufacturing specifications.
Assuming the drive spins back up after being left in a cupboard for 15 years, if you're still even able to find a computer compatible with whatever cables it used back then. But yeah.
If proper SATA ever goes away, I'd wager that there will still be SATA-to-USB adapters on sale. Heck, people still find ways to connect floppy drives to their modern PCs.