Source is KeplerL2, who is generally considered a reliable source for insider hardware info, particularly on AMD GPU hardware and AMD SoC for consoles.
Previously I would have personally estimated Steam Deck 2 to release mid 2026-early 2027, but the recent info about an upcoming Steam Machine made me think that maybe I should push back that estimate.
Of course even if we assume this is reliable insider info, a lot can change in couple years, so things can definitely change.
They aren’t going for detachable controllers, most likely. Theoretically they might make a future screen + SoC modular so you can swap a frame (it would kinda make sense from an engineering perspective to build the center similar to a tablet IF you can hit all required specs that way), but even for Valve that’s unlikely. They may prototype it but likely won’t release it.
Would OTOH be nice with a Steam Controller 2 which can fold flat to fit in the same case as the Steam Deck. Also not likely to happen 🤷