It would be great to be able to do a master freeze with the ability to thereafter add more audio tracks to the session which can be recorded on while the master freeze still exists for the purpose of easing the CPU while tracking.
Having an ability to also export this freeze to an audio track would also be great and also to decide if the freeze happens post or pre master inserts/fader.
This would also be great for just listening back without having to do a master export to audio track. As well as doing stereo master prints - especially if you could freeze post or pre master fader/inserts. If pre, you could continue to tweak your master insert plugins whilst also going through hardware.
Or, if you have been mixing as you go, and have built up a load of plugins on the CPU, and then you want to do some more track, but want to lower your RAM memory setting for less delay. Sometimes I run into this, and going channel by channel, slows down the session.