So basically it's a computer. As in normal desktop computer where you can replace parts with a little effort. Need more powerful cpu? Just buy a new (compatible) one, unscrew the side panel, take old cpu and cooler out and put the new ones in.
If this was cheap (compared to a desktop), it might work. But 850 bucks and you get what? A smaller case.
And where does that "normal PC has a 5 year lifespan" come from? I'd say people upgrade their computers around that time for more powerful one - not that it doesn't work anymore or it cannot be fixed easily. I think I have two or three 10 years old machines laying around and they work just fine.
Normal desktop PC:s are built for easy repair. It has under than 10 parts which (most of the time) all are user replaceable. PSU, CPU, Motherboard, Memory, GPU, HDD, Optical drives and possible addon-cards.