From the Source engine updates analyses, I think it’s going to be voxels (thus deformable world), a physics engine to support voxels, fluid stimulation, fire simulation, acoustics simulation, NPC AI emotional simulation and adding senses like smell to NPCs.

Force feedback codpieces.

... smell-o-vision.

Gameplay that can support wiiU esque format with a steam deck and a steam machine? And a steam frame? I dunno

Steam consistently have been pretty anti-AI, not banning it, but heavily suggesting not to play games which use it.

So very much doubt AI.

If anything it would be Source Engine updates, HL1 was an elaborate tech demo, at its heart. As was HL2, to a lesser extent.

If you can imagine it, then its not worth it. :p Half-Life 3 will be unimaginable... I mean off course it will, yes?