Valve don't seem particularly inclined towards the HL franchise and haven't been for a long time. Do you have a source for that claim?
Gabe Newell talks about abandoning the episodic schedule here: https://www.develop-online.net/analysis/the-valve-manifesto/...
My assumption has been for years that "HL3" is as much a joke inside Valve as it is outside of it.
> Gabe Newell talks about
This was six years ago.