It looks like this guy amar on Neogaf has some Gran Turismo inside knowledge and he made this cryptic post today, looks like the reveal of the next game might really be almost upon us.
"So,
Gran Turismo Sport
Interesting"
http://m.neogaf.com/showpost.php?p=164411748
Edit: New post saying that GT won't be at E3:
http://neogaf.com/forum/showpost.php?p=164552046&postcount=8365