Great idea! Though ideally there should be a notice dialog to alert people that they're participating in a beta.
Perhaps this should be internalized in Valve's bug tracker and closed here as this is not a OS-specific feature request.
Nothing extracted yet.
Please consider automatically opting-in the user to the public beta of games when the main game cache is empty and a public beta of the game exists. Ideally the should also automatically get switched to the non-beta once content exists. The beta select should probably read 'NONE' with a message letting the user know that public beta is temporarily enabled.