I don't think VAC is updated with goldsrc cheats, so i don't think a speedhack blocker feature gonna be taken in account.
And anyway, speedhack is easy to detect by other player, and not the most "destroying game" cheat, by far.
Let's see...
This has nothing to do with VAC. Such old engine exploits such as speedhacking should have been blocked a long time ago with proper game server code. It shouldn't be possible for the player to move faster.
Nothing extracted yet.
HL1/CS already has some sort of anti-speedhack code, but it doesn't work correctly. All it does is making the speedhacker lag once a while.
As you can see, this was added a very long time ago:
Maybe the default value could be changed to really block speedhacks, or a real speedhack block could be added. There are already some plugins that do it correctly.
Speedhacking works by sending more command packets than necessary, so it just needs detecting how much packets/sec a client is sending, and blocking him if he sends too much.