Can't be GTA6 since they only work in one game at a time and that game is RDR2.
I don't think MS would give their big E3 reveal away.
With the leaks, it makes sense if it's Soul Calibur 6.
I can't see it being MGS6 considering they have been working on metal gear survive. Secondly, Keighley worships Kojima. The likely hood he would give Konami the stage to show off MGS6 is zero.
Whoever said life to be like a box of chocolates clearly didn't know what he was talking about.
Life is more like a game of bumper cars. At every turn there is a possibility you will get screwed.