There wouldn't be a "deadline", exactly. It's possible that RIM may encourage developers to submit apps by a certain date so that they'd be available on launch (as they did before the PB OS2 release), but if a dev misses that deadline all it means is that they get a later release to App World is all.
Originally Posted by blockbuy
Considering this is an upgrade that I'd term "significant-but-not-major", I don't know if there will be any special push here. Pretty sure we'll see one for BB10, though.