Probably not, unless they learn to count to three, those series seem to be over.

Valve seems to be more of a platform company these days (a very good one, though).

Remember Valve released HL: Alyx to promote their first VR headset.

It is not unreasonable to get a pair of titles to promote these two new products.

A man can dream, but a new HL for the Steam Machine and a new Portal for the Frame would be great.

It would also be the biggest sales pitch in the universe

"Buy a Steam Machine and get Half Life 3 for free" "Buy a Steam Frame and get Portal 3 for free"

Tech and software support should be absolutely perfect though..