AFAIK the NG had a single motor, but separate inputs from the FCC and the pilot (
Why are they called pickle switch? Looks it up. Seems like it was the name for the bomb release) wheel mounted trim switches, a separate path. Anyone with an NG FCOM see what it says to do with trim runaway?
Separate trim channels would not have helped Lion Air as the flight that was successful was fine with manual trim and it would not have helped the accident/crash as they didn't use the cut out switches at all. It might have helped ET302 but they had failed to use the wheel mounted trim switches properly even when they were effective.
Had the logic been to invalidate the AoA when the vane heater continuity failed then ET302 would not have crashed. For Lion Air invalidating both AoA sensors due to disagreement would have worked. In both cases,
AFAIK, all systems depending on AoA would have seen the invalidation and ceased all automation and Lion Air would have also been fine.
The other change I would look at is adding a vane stop that is in a shorter range than the counterweight stop. If the vane is destroyed then the vane stop would have nothing to stop against allowing additional travel. Even a momentary excursion into that area would be used to invalidate the AoA sensor. It might also serve as a check on the electrical setting as only a few degrees of additional travel would be used - so a check of the electrical vs the mechanical would form a barrier to the Lion Air electrical mis-calibration and would make for a simple test on a replacement - if the AoA system goes invalid when moved against either (or both) vane-stop then the sensor is suspect. This would have also prevented the Lion Air crash as the miscalibrated sensor would either be caught at the factory or could have been easily caught by the maintainers. It would move the failure to setting the wrong requirements for the sensor - and that could be caught with marking on the fuselage for the sensor vane travel limits.
For all the "but they hid it" about MCAS, the FAA would not have seen the AoA subsystem flaws fixed. All the FAA would have done is to ask for more paperwork; there is no indication anyone felt that the trim runaway procedure would fail to be used. Certainly after the Lion Air crash I didn't see any news of 737 MAX pilots refusing to fly, maybe in private? I believe no CAA grounded the 737 MAX after the Lion Air crash, even after the preliminary report made clear the human factors problem. Grounding only happened after ET302, suggesting a general opinion that the failure mode was expected to be handled as a trivial or annoying matter, the way the first Lion Air crew did, and that inexperience and lack of familiarity was the main problem, one that was solved with the Emergency AD.