At least they're still giving away source-code, which is rare these times.
And using Metamod Source I'd think you could hack your way into a lot of stuff. Probably not with as general functionality as with the old SDK but nevertheless...you could if you wanted to.
Speaking of hacking into it, has anybody else noticed the disappearance of the BotController in TF2 ? Don't know if it's back again with the new beta sdk for orange box but if it isn't this could mean either a revamped shiny new bot interface or totally removed bot support.