This seems like a cool idea.
As Eli mentioned, parkour isn't all too popular a gamemode on Cube as of now. Imo, some reasons for this are the balancing of difficulty and it's 'finiteness'.
What I mean by this, is most players are either
(1), skilled enough to finish the parkour (and then have no reason to play that gamemode anymore).
Or (2), struggle with it (I'd guess this would be the more common of the two) and have no good reason to continue playing it.
I can't think of a perfect solution to this, but this suggestion is promising. I can see it providing a solution to both cases above.
Obviously, there is competitive parkour (I believe only on bedrock currently?), however this becomes incredibly repetitive / easy after not very long imo, and I struggle to see it as something that would do well at retaining players? Hence, I don't really think it does a good job of solving (1) and (2).
In terms of originality, Reesle mentioned this general concept has been implemented on Galaxite already. This is a bedrock server. I can add that in addition, I know of a Java server (Minr) which uses this to some degree. It certainly wouldn't be the first time it's been done, however I agree with Eli - why is that an issue? The playerbase is largely disconnected from other servers. I've seen parkour grow steadily more popular on Java recently (although not on Bedrock yet, admittedly) so maybe now would be the time to try something like this.
Of course, this would be something of a leap of faith given parkour's current state, and potentially difficult to implement? I'd guess it's unlikely this would be added, but I still think it's cool nonetheless :)