I don't see this selling all that well.
The design doesn't seem like something that will have the mass appeal the Switch's design has with the ease of 'switching' game modes as well as the detachable joycons. The look is also less appealing. I get that they want to say it's a portable PC, but it's bulk is giving me Wii U gamepad vibes.
The price is going to be a tough nut. It's lowest-costing model is $50 more than the premium Switch model, but that's going to be compared more to the $300 base Switch, not the OLED model. The $529 model is going to make the $350 Switch OLED look more appealing to the general consumer.
My guess is Valve is courting the high-end PC gamer market, the guys who spend fortunes to build their custom rigs to be as powerful as possible. But I'm not sure it's powerful enough for that. The RAM is astounding and on par with current gen, but the rest of the specs are still decidedly last-gen, meaning it still won't run current-gen games as well as an actual PC or the current-gen consoles and will have problems similar to what the Switch had with PS4/XB1 games, and I'm not sure the PC master race crowd would settle for something like that even if it's the most powerful handheld ever.