Sony already has more than enough AAA exclusive games already announced to cover up for the rest of the year (Spiderman, Detroit), 2019 (Days Gone, Dreams, Ghost of Tsushima) and 2020 (Death Stranding, TLOU Part 2), so they dont really need it, and thats not counting whatever they announce this year or the next ones, plus the typical japanese exclusives they get every year like Yakuza, Trails of, Nino Kuni etc, (granted some of them end up on PC and some of them dont).
Nintendo probably had the strongest start ive ever seen of any console, kickass hardware and kickass exclusive one after the other, and i think this E3 is gonna be essential for them to keep the momentum they have builded up so far.
Microsoft does need some great announcements but to be honest at this point in the race its not like its gonna change much (we are just about 2 years away from next gen), still i do believe they should support their system until the very end.
