Haha no kidding. The "gameplay showcase" is an empty room with some random objects dropped in it showing absolutely nothing that wasn't already in HL2 in 2004?
There's zero chance of a C&D. Valve OK'd this project long ago. The Black Mesa developers sell the game directly on Steam, and Valve are well aware of it and allow this group to continue to make money of their work:
This is for the HL2: Episode 3 remake, and not the Black Mesa fan remake. Sorry. I am a bit off. I saw some triggered reactions in my bell icon, and I assumed it was for that other "Black Mesa" Zen thread that popped up recently. Then I started reading the comments about UE4 and Episode 3.
I actually forgot about this fan creation of Episode 3, and that it is using UE4. But I think Valve probably let this one happen too.
I'm thinking Valve is watching this project very closely and if they end up liking it, they'll buy it and/or offer the devs jobs at Valve)
and offer it as an "official" Half-Life 2: Episode 3 game.