It'll be called "V", which is short for Vegas AND the Roman numeral 5.
It'll include every single script that's been written for Vegas.
Editing templates: Select a mood/genre/transitions and let her rip. It's rendered in the morning and burned to DVD in 5.1 with menus!
Unlimited UI customization options.
Keyboard shortcuts for the phone numbers of every studio in Hollywood.
There will be other improvements, but I won't list them since they're so incredible, you probably wouldn't believe me.
Support dual processors, support 64bit, fast rendering (realtime rendering) times, ability to support larger preview windows--without dropping frames.
There's still plenty I haven't tapped into (even after three releases)--but speed will shut up the Premier and reviewers comments.
Of course...there are a few more things I'd like to see... (like an aggressive upgrade price to the faithful followers for the pre-release (Premier Pro upgrades for $199))