I'd be interested in hard insights (maybe it would have to come from levels.fyi or LinkedIn) like monthly charts of: number of new hires, salary&TC distributions, title or skillset distributions, by company/industry/size per month.
And similar monthly breakdowns for ended employment.
Internal promotion numbers would be great, too (and good incentive for employers to give attention to promotions and retention, rather than the fad of transactionally renting team members for only 18 months), but maybe harder to get.