Ok, let’s suppose you have a big project with tons of tracks and vstis… Soon or later your cpu will be on its knees.
Time to render !
You render your vstis to audio track, disable the original vsti track to save ram and cpu… and then ? DO you put the original track + render in a folder (what i’m actually doing) called “drums”, “bass”, “piano”, etc ? You’ll quickly have tons of folders and tons of clics to open/close those folders (what i’m actually doing).
Could be really handy to have an option, in the render dialog box (for example), where you can link the original vsti track to the rendered audio track, and disable & hide the original vsti track.
The disable & hide feature is already here, only the “link” functionnality is missing.
Sudio one/presonus managed this situation by converting the vstis in audio on the same and only track.
Any opinions, ideas, workaround welcome ! 
I was thinking something similar. What they should to is have a little button on all rendered parts called “Revert.” When you press “Revert” it turns back into a midi track, also another button which will extract the midi to a new track in case you want to use it for doubling for instance. The midi from rendered parts should always remain embedded in that part for future use. You may decide years later that you want to replace that piano with a better piano.
Render is a wonderful feature but we could make it better.