Until they find a way to make a breaking board react like a gun left on the ground to the client, so that it doesn't eat up packets like an actual player model moving around, there's no way that HL2 is going to be multiplayer.
See, the problem with your argument is that even in the ripped/stolen/raped/leaked/whatever the fuck you want to call it build of HL2, multiplayer was present. And you know what? It was functional. Oh sure, the player models where nothing but spread eagle stone statues in a boring gray tone of Freeman, but the multiplay was there. Over internet it was choppy, over LAN it was smooth.
I guess that just about proves you wrong, doesn't it? Why would they have a functioning netcode in an alpha
of the game, and not now? The answer : they wouldn't.
You're done, bye bye.