I would really like this a lot, especially since I do a lot of drum synthesis with Overtune + Renoise FX, and when rendering these short samples out I always have to use the Auto Gain Correction that is on Master Track only. Then when I render the drum sound I’ll have to copy the PostFX Gain from Master Track to e.g. Kick instrument track and all send tracks it uses, to render kick sample out correctly (since even when selecting with Alt+W, render selection to sample will not take into account the Master Faders). A way to select multiple tracks and adjust their volume together would also form a decent solution for this problem.
The workaround now for when I use e.g. 3 or more different sendtracks is just use Render Song dialog, making a 2 beat pattern with just the kickdrum and loading the sample back in for adjustment. Only thing is, that is much more annoying (under linux) with selecting file location and name (indeed the end goal is to have a kick drum sample normalised and trimmed saved as a .wav, but exactly how I hear it in the song).
So I would like a AutoGain button on every track, where maybe in the mixer the fader (not meter) gets a weird color for a second when the autogain kicked it back.
Edit: in my default start song I do have a MixDown send track so I just found out I actually have to copy/paste the postgain value only once. That helps.