Spinning rust is still useful for many purposes and will probably live on for decades more. We generate a ton of data and most of it ends up as read rarely or never. But it can live with slower access times on longer duration storage.

It’s honestly just like tape. There will be an HDD market for a long time that will be hidden in the whirl of data centers. Consumer HDD will slowly melt away, but the price/byte and durability of disk will keep it viable for quite a while. It’s still faster than tape (but not as cheap).

That's actually a valid reason to spin off a business, especially if you happen to know you'll cross the inflection point in ~5 years. It isn't the same as the "legacy liabilities" game, though. Some investors want the growth business, some want the stable business, some want a cheaply-priced declining business (seriously; look into anything that pays royalties).