(Disclaimer: moderators are volunteers drawn from the forum community, we are not Bethesda employees and as such are not privy to any details that haven't been released to the public. The following is personal speculation, nothing more.)
Bethesda does have a pretty full E3 line-up, which may mean they're holding off on more id-related announcements for QuakeCon. On the other hand if they had a secret announcement prepared for E3 we wouldn't know about it beforehand.
