Not only get it out but actively promote it as an opensource project instead of proprietary and make revenue through an asset store. Theres so few games that use source that theres no way its commercially viable on its own.

Valve doesn't do it that way. Instead of some crummy asset store with generic and terrible looking assets they literally just let you use the assets from their games. See Garry's Mod, Sven Co-op and Insurgency for an example of this.

Yeah I meant in addition to their own assets, hence the revenue stream. A standard setup like Unity has for their asset store.

Using unity as the example there are some crummy assets, but there's also some incredibly popular and well made assets, many used by AAA games.

Valve is not interested in games, only steam. DOTA 2 (2013) was their last mentionable game.

Half-Life Alyx*