The ability to give a course a difficulty stat, I assume it will be used purely for cosmetic purposes, and to be used in placeholder APIs using @steve4744's plugins.

Question is, how will it be configured.

1. Same as Ranks, where 1 = &4Easy, 2 = &7Medium, 3=&6Hard, then you do "/pa setdifficulty (course) 1", etc.
2. Predetermined difficulties such as "/pa setdifficulty (course) hard" which I suppose could have a string.yml for what "Hard" looks like.
3. Each course can have a completely different difficulty "/pa setdifficulty (course) &4Super&6Hard"

Any ideas?

After a quick thought, having global difficulties from 1 to 5, then each of these would have a string equivalent in the strings.yml.
Example could be "/pa setdifficulty (course) 2"
strings.yml:
"Difficulty.1=&1Very Easy"
"Difficulty.2=&2Easy"
etc.

Maybe the difficulty statistic could be calculated automatically?
For example you could take into account how much time does it take to finish the course on average, number of deaths compared to other courses on the server etc.

Calculating and displaying a "median length" of a course or something similar could be helpful too.

This is very neat feature that could be added. definitely adds value to the Parkour! and on top of that, if it could dynamically adjust rewards (money for example) based on difficulty.