I think not being heckled, abused, or harassed will have a positive impact on most players. Though not all.

For some (and I mean in no uncertain terms, for black players and those from other minorities), it's probably a godsend, and that sense of 'relief' probably does have a measurable outcome (i.e. some players raising their standards, and others doing likewise to follow them).

OPTA and their like measure a lot of data points. So this hypothesis could probably be proved. Passing percentages, XG and assist rates for example, but I'd reckon individual running distances will be a particularly interesting metric to explore.

Any of those stats could go up or down for all players, but I do suspect there will be observable changes, because of these new playing conditions.