From a photography standpoint, autosnap is probably the best option to use. If your exposure settings were already correct before autosnap, you get your photo. Else, you still get photos while AETTR is doing its calculations. ie: You don't miss your moments.
It would be handy to have autosnap linked to set/half shutter. In this way, when needed you can press set/halfS have have autosnap perform its actions, but most importantly, the setting is then reset back to a state where it needs set/halfS to trigger the operation again. This would save having to enter the menu to disable autosnap, or, running around in autosnap mode killing the shutter.
All other options, link to dualISO, SNR limits etc would remain fixed at the last calculation.
Where lighting conditions change significantly, AETTR would be a quick exposure option where images are still taken while the calculation is being performed.