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.
Why would you need 1440p on a small screen like that? I think 720p on the original switch was fine and see no need for anything with a small screen to have so hig resolution. Especially since that means less battery time, just waste of power.