Valve will loose competition quick if they wait that long. Asus is probably already working on a rog ally 2, legion go came out and is packed with features. Aleast release a steam deck with the newest GPU, ram and a 1080P 120hz or 144hz oled or QHD 500 nit screen within a year or so from now.
It’s because Valve are targeting 15w max with 10w as a sweet spot. Where as Legion Go/Ally targeting 25w with a sweet spot of 18w. They want a handheld that appeals to mainstream audience, while other handheld OCs are more powerful the battery life isn’t sufficient for mainstream audience where you will mainly be restricted playing near an outlet. Currently there is no new chip that is more powerful as can run at low watts. Will take many years for this to happen