It's like vehicles. Desktops/workstations and even most non-tablet laptops are now analogous to small trucks such as pickups. Tablets and phones are cars. Most people drive cars. Trucks are for work or people who like to haul stuff.

Servers and huge workstations I guess are like 18-wheelers and locomotives. :)

The "mobile is the future of everything" people were wrong. It's not that desktop is going away, but the market is re-segmenting. Most casual users don't need a desktop. They just need a UI device that can run apps and access services. So you now have a bisection of the computing device market into pro/workplace type devices and casual user devices. I suppose there's a third category too: hobbyist and enthusiast devices. That's where I'd put things like the Raspberry Pi or more techie geared laptops that run Linux.

I predict that rather than converging with mobile, desktop will actually pivot more toward pro, developer, and power user needs. Apple's recent 16 inch Pro release is a baby step in that direction on the hardware level. You'll probably see it at the software and OS level too. Desktop might actually shed a little bit of its user-friendliness gloss in favor of being unabashedly "pro." "If you don't want to know what a network, a folder, a file, or an IP address is, get a tablet."