Thank you for your answer, infos and the link.
Regarding on programmed obsolescence, I tend to believe that there is a implicit contract between the buyer and the vendor, on how long the product should last.
As it is not formalized, even explicited, there is room for disagreement on the "terms", and in consequence , for dissatisfaction.
Apple used to build machines (computers) that would last easily 4-5 years, and obsolescence would come because mostly of needed software upgrades. You paid for what you had for, and if you needed more, you had to pay more. Fair. I have a 23" screen which is 8 years old and still very good. I still have Apple computers that come from the 90's and can boot and perform as they were when i bought them.
With the smartphones, they began to see it differently and began to manufacture things that have a much shorter lifespan. The contract was still in a way respected, as people expected to keep their phones for 2/3 years. (I won't bragg here about the 1rst iPad who was nearly unusable after 18 monthes and pushed OS upgrades)
My take is that they have applied to the Time Capsule a phliosophy of the smartphones, and they broke the implicit contract.
Backup is in the realm of computers.
You expect your backup to last as long as your computer. And when you build a software solution for backup (Time Machine) you don't force an hourly backup if your hardware can't cope with it for the required time.
Especially, backup implies reliability, so they are all the more in red zone.
Mixing backup, storage, router, firewall, wifi functionalities as they did with the TC is not an excuse in my opinion.
Having said that, and coming back to my own issue, you seem pretty knowledgeable about this subject and convinced that this is the warning of a announced power unit failure. Right ?
Now I will read your site and decide what I will do, as of course the 500 GB drive in it is a little too small for my usage now, and would have preferred to go for a 2 TB :-)