We emailed Walker for further confirmation, and he went on to explain:
We are in the process of getting it all done. It’s a bit messy because we have multiple versions of the SDK, and there’s some dependencies we need to shake out. But yes, the gist of it is that we’re just going to go ahead and make the Source SDK freely available.
So that's good news for, well, everybody. You can read more about it over at Rock, Paper, Shotgun.