I think the only way to get Offset control is to see if we can get ZWO and QHY to put their backing behind having it added to the ASCOM spec. That seems to be the only way the ASCOM developer(s?) would be willing to invest the time, if there is manufacturer backing. I think it is indeed a critical factor now for CMOS cameras, given they have both adjustable gain and offset.
That said, in the mean time, it should be possible to find a "happy medium" offset that would work for all gain settings, if you really needed it. Personally, because of some strange gain/banding issues at very low gain settings, I don't really use my ASI1600 below Gain 76. I did some evaluation of a bunch of additional gain settings, and found that 76 gives an FWC o ~8192e- with read noise of ~2e- and gain of ~2e-/ADU, which delivers exactly 12 stops of DR. Combined with the 12-bit ADC units, this is basically the sweet spot for the camera. I used an offset of 15, however I think it would be just fine to use an offset of 20 or 30. At an offset of 30, I think you would be good to image from Gain 76 up through Gain 200, which is quite a range (gain goes from ~2e-/ADU to ~0.5e-/ADU).
The difference in read noise from Gain 200 to 300 is about 0.15e-...not really enough to fuss about. So I think you could actually have quite a bit of success with just configurable gain in the sequence editor, by using a fixed offset of 30 ADU. Set it once in the driver, and forget it. It sounded like the SGP devs are certainly open to adding gain as a first class option in the sequence editor (I started a thread bout that a couple months back and it seemed well received). I hope it's still on their radar, too! I am hoping to get into some more LRGB as fall rolls in later this year, and it would be really awesome to be able to set gain for each filter...use a low gain for L, bump it up a couple notches for RGB and stick with a consistent exposure for all filters.