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Certainly not all discretion, but things can be advanced in the right direction. Sensors in the balls, between the first down markers, under the boundaries of the field, and under the goal lines. Automating calls relating to these would be more impartial than refs, just like automating ball/strike calls in baseball would be. But automating judgement calls and personal fouls would seem impossible to implement.
I think MLB and the NFL should do everything they reasonably can to automate what can be improved with automation. I don't think they've gone nearly far enough. To me if you automate calls that can be achieved through automation that's a lot of boring, time-consuming replay reviews you avoid.