This seems like a very serious move by Valve. Not off the shelf parts but a custom APU, it must've been challenging and expensive to develop.
IGN also notes that unlike the Steam Controller and even though they had doubts about the button placements it is very comfortable to use.
The key here is performance, how much of a 'hit' will it take compared to optimized console games. At 800p they certainly have a lot of leeway but docked might not yield the same results.
I also wonder if they're going to do something about optimizing delivery like the Xbox systems do. After all at 800p you don't need 4k texture packs and that could save a ton of storage.
I know that early on in the Switch cycle quite some people who were PC-only bought it to play BOTW but also the games they would usually play on Steam portable like DOOM, Diablo III and indies.
It always surprises me how every PC gaming Switch owner I know has a vastly different library of mostly their favorite games but the ports have become less interesting as the Switch has aged.
Far less expensive than a gaming laptop, much easier to carry. If the battery power indeed holds up (2 - 8 hours is mentioned in the specs) this could finally be Valve's big break in the console hardware market.
Plus it runs Windows, so also GamePass, EGS and Xbox Cloud.
A Switch for adults