Thanks Sam.
With regards to shifting bits and dynamic range, here is my opinion from 25 years of imaging (both pretty picture and scientific). I have respect for you and ZWO and I hope this does not come across as me preaching but this is a very important point to make.
The most important unwritten principle for most of us who use dedicated astro cameras is that the output should be untouched / unmodified / RAW to the largest extent possible. This and cooling are the two most important reasons we pick dedicated astro cameras over DSLRs and video cameras where the in built DSP wants to decide what is best for the user.
Also note that there will be
A 16 bit image can fit 2^16 = 65,536 levels. So even x4 bin (sum) output with a 12 bit ADC will fit in a Mono16 format.
Single exposure x1 bin = 2^12 = 4,096 levels
Single exposure x2 bin = 4,096 x 4 = 16,384 levels
Single exposure x3 bin = 4,096 x 9 = 36,864 levels
Single exposure x4 bin = 4,096 x 16 = 65,536 levels
There will be no loss of dynamic range even with x4 bin.
But ultimately the most important principle is that the output should be as RAW as possible. The decision of how to deal with saturation in extreme binning situations should be left to the user as there may be use cases which you cannot envision (Photometry is just a more obvious example).
