definitely up for discussion, but I'm not even sure if this shouldn't be moved to the Cab block, or added to the Cab block as well. for some reason I associate that effect with a speaker...
That makes some sense from a user standpoint, but I don't think it works from a technical standpoint. It basically has to add that signal back into the front end of the Amp block. Having it in the Amp block means everything is contained within that block. If the control is in the Cab block, then there are ways it could get weird/complicated. What if your amp is running into 2 cabs? What if two Amps are feeding into the same Cab?
Also keep in mind there are other speaker characteristics that are modeled in the Amp block currently, like the Impedence mismatch and Speaker Resonance. It's done that way because it works better from a technical standpoint, even though it logically seems like a Cab characteristic.
I definitely agree with the general sentiment that this feels like a really important, fundamental function that should be more visible/accessible than other deep editing parameters in the Amp block.
I think it might be cool to have a global offset control, similar to what we have for Reverb, noise gate, etc. That way you could map that control to Perform tab and adjust all your amp blocks/channels with one knob on the fly to suit the venue.