There are whispers and speculation but I can tell you Cyberpunk 2077 will definitely not be at E3 this year. That comes from the horse's mouth: CD Projekt co-founder Marcin Iwinski himself.
"It might happen that we will be at E3 and we will show something at E3, but I just want to make it clear it's not Cyberpunk," he told me at Polish conference Digital Dragons recently. "We still have a lot of work to do with Cyberpunk."
I believe what CD Projekt Red will announce at E3 will be the game - or thing - it mentioned in a recent annual report. Under plans for 2016, CDPR mentioned, "A new type of video game format previously unexplored by the studio." That doesn't necessarily mean it's a game and doesn't necessarily mean it's coming out this year. But it could be both.
When I asked Iwinski if it will be this thing at E3 he said, "We will see." When I asked if we'll find out what it is at E3 he said, "Well, hopefully." And when I asked if it had anything to do with The Witcher he said, "Time will tell."
http://www.eurogamer.net/articles/2016-05-25-cyberpunk-2077-e3-cd-projekt