I'm looking for it as a general development machine, sometimes I do stuff that requires GPUs so if they can get a competitive price wrt. building a custom PC then I'm all in for the convenient form factor!
"Proper" is very subjective here. My entire workflow for developing 3D engines is covered a couple of times over with the announced Steam Machine specs. In fact, even when I was working in web backend development it would've covered it as a dedicated development machine and that was with some pretty pathological dev setups, language servers that ate up way too much memory, etc..
It's a laptop APU with graphics card moved to a daughter board, hence "semi-custom".