Frank
If I take my race IDs there were 1,274,775 races in the 51 days between yesterdays China and the one last season. That makes pretty close to 25,000 races per day on average, so even a few MB sum up into considerable amounts pretty quickly. Now storage space isn't that expensive, but the servers have to be scaled to save, backup und, foremost, deliver that data as a race replay upon request.
It'd be nice to have race replays, but the best chance to get this would be as an extra perk for some kind of game supporter subscription or other long term deal.
Of course one would pay for these replays. Regarding storage that's not an issue, cost is cheap for high performance storage. That said, it all depends if devs want to add the feature and the priority. Based on my posts in suggestions forum they don't engage much as they are probably already swamped. So we all just have to wait anyway.