You've mentioned gain structure a number of times in relation to pan law and stressed the importance of pan law upon it. But I have to disagree. You have to understand that the pan pot is the LAST thing in the signal flow of a channel. ALL processing on a channel, including the actual fader, happens BEFORE the pan pot. This goes for analog consoles and their DAW virtual bretheren. So clearly, pan law will have ZERO effect on gain structure at the channel, or any of the inserts, or any of the sends. It would only affect things after the pan pot which would be any downstream busses. I would consider this an incredibly minor issue for two reasons: first, we aren't talking about a lot of different, a couple dB at best in the center. Nothing that will rock any DAW's world to say the least. Second, because you balance BY EAR you will compensate with the fader anyway. So after the pan pot at whatever downstream buss (either the 2buss or some group buss inbetween if the situation calls for it) the actual levels will be the same REGARDLESS of what pan law you are using. So the ONLY place pan law will affect gain structure is between the fader and the pan pot. And trust me, I have never in my life heard of a pan pot being sensitive to gain levels. Certainly not in any DAW and honestly, not even in any analog consoles.
So just to be clear, a pan law will have ZERO effect on gain structuring of the channel and any processing on the channel because the pan pot (or pan knob, if you will) is AFTER all that stuff including the fader. Pan law will have no effect on anything after the pan knob because anything after the pan knob will be a buss of some sort and you will already have adjusted the (pre-pan) fader to compensate for whatever pan law you use, thus giving you the same output after the pan knob going into the buss. The ONLY way pan law could affect gain staging is post-pan and pre-buss if you balance levels by putting all your faders at pre-determined positions without listening to anything - then you could wind up with different levels on the front side of the buss depending on which pan law you use - but NOBODY mixes that way because it would always sound like ass.
I'm sure if you tried really hard, you could do some crazy signal routing that would cause pan law to affect gain structure inadvertently downstream - but you'd have to really try.
Anyway, I'm really not trying to be a dick (although I think I sound like it). I'm just trying to help you understand these audio concepts and break up some erroneous misconceptions you have.