Current California regulations for remote operators are identical regardless of whether the car is considered SAE level 4 or 5. I'm not sure what constitutes "continuous monitoring" there (I could interpret that as anything between eyes on road at all times down to positive SOH messages arrived).
Apart from regulations, level 4 doesn't require a remote operator monitoring at all times. It just requires them to be available when the car recognizes it can't handle the situation. Depending on how frequently interventions are needed, that could mean a remote operator for every car, or one for every 10 thousand.
The important part about Level 4 is that the car recognizes its own limits and doesn't act outside of them. How practical those limits are is completely undefined by SAE. Level 4 is a continuum whose limit is level 5. We will definitely be seeing practical commercial value as we approach level 5 but haven't yet gotten there.
Apart from regulations, level 4 doesn't require a remote operator monitoring at all times. It just requires them to be available when the car recognizes it can't handle the situation. Depending on how frequently interventions are needed, that could mean a remote operator for every car, or one for every 10 thousand.
The important part about Level 4 is that the car recognizes its own limits and doesn't act outside of them. How practical those limits are is completely undefined by SAE. Level 4 is a continuum whose limit is level 5. We will definitely be seeing practical commercial value as we approach level 5 but haven't yet gotten there.