Valve has work left to finish on the Steam Deck, and I think most of that will be on the software side. The hardware isn't quite final, but I expect only small changes that affect manufacturing and reliability, not design. SteamOS 3's new design looks great, but it isn't as seamless yet as a console UI. Valve still has months to left to work out those bugs. And for the most part, it just worked.
After spending a far too brief couple hours with the Steam Deck, I'm not sure if I would consider it a one-to-one replacement for the Nintendo Switch. Its bigger size isn't as ideal for throwing in a backpack and playing on the go. But as a portable PC gaming machine, it really is impressive: it's comfortable, feels great to hold, and seems to have the power to play games like Death Stranding with decent settings. If SteamOS really can deliver the compatibility Valve's aiming for, the Steam Deck is going to become my go-to system for playing games that I
wish I could play on the Switch, lounging on my couch, that it just doesn't have the muscle for. And
I'm convinced it's going to be the best emulation device ever made.