Valve will officially let you install SteamOS on other handhelds as soon as this April

? How so?

Valve didn't prove Steam Machines, didn't really market them, and game support wasn't there, they just launched it with a promise to fix stuff.

They did the opposite with the Steam Deck, they proved the concept with their own hardware, they marketed them heavily, and they had a ton of games ready to go at launch.

They learned from the mistakes made with the Steam Machine.