How pronounced is the difference if we would change the running direction for runners?
Been a sprinter for 12 years, so from that perspective, I don't think it would matter. The angle that you take when turning is not drastic enough to have a musculoskeletal difference; step height differs only a few inches. Additionally, turns never account for more than 50% of a race (barring a couple distance events, where turns act much more like straightaways anyway due to the lessened speed), so a bigger imbalance would be disadvantageous for straight sprinting. In practice, I think it would take a little bit to get used to, but not more than a year.