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.
So basically when the hardware gets better and cheaper, like AAA games on medium 120fps stable, additionally it would use MicroSDexpress cards. Oh, and HDR and dynamic framerate on OLED (both at the same time) needs to be developed for small screens.