Werewolf: the Apocalypse - Earthblood. Cyanide confirmed that game will be at E3. They are also working on the adaptation of Paranoia, but I dunno if that'll be at the show. But Werewolf is, and along with Bloodlines 2, that makes me pretty stoked to see more.
Hopefully Bethesda has something new from Arkane studios and/or Tango Gameworks. It's been a while.
Microsoft should hopefully also say something about Age of Empires 2 DE
-in the same vein, EA might show off the remaster of Command&Conquer, and Ubi has the new Settlers game releasing this year....
Remnant from the Ashes, a post-apoc schlooter from Gunfire Games published by Perfect World should probably make an appearance since it's coming out in August.
Dontnod is likely to make an appearance. A Life is Strange 2 update is practically guaranteed to be a thing at the Squeeenix showcase imho. But Dontnod is also making "Broken Mirror for Bamco
-And Speaking of Bamco, Man of Medan got a release date. Maybe it'll be playable at the show?
I will be incredibly surprised if either S.T.A.L.K.E.R. 2 or 4A's new IP makes an appearance. But it's not impossible, I guess?