Still not possible to freeze multiple tracks at the same time? This function will be very helpful. I am not too crazy about 'Duckbar'.. 
 
 

You can use in Track View, under Tracks, "Bounce to Tracks", to achieve a midi render that is equivalent to freeze -- the benefit of this is that you can select whatever tracks you like and render them at once into a single audio track.     Be sure to select both the midi and the 'instrument' tracks that have the VSTi outputs.  
 
There are some issues (imo) about how Bounce to Tracks (and freeze) work .. so be sure to review the result and get your options set to suit.