I can't see why this system couldn't be used anywhere[?]

The only adjustments I'd make is 3yrs to 5yrs rather than just over 3yrs. Past 5yrs horses don't generally sprint as well as they did as 3 to 5yr olds [just like us].

"One of the top 5 jockies for the track" [see grandracing and sports], so the system could be used anywhere and I'd shorten the days since last start to 21 days.

Finish position is a hard one. I know punters point out lengths from the winner is more important that finish position, but there are so many slowly run races nowadays and they naturally produce a lot of blanket finishes. 4 lengths from the winner could easily be the last horse home.

No worse than 4th. in a similar prize-money [or more] race sounds like a more reliable rule overall.