I don't think the class example works, because you wouldn't operate on a class hierarchy in code. Pipes is all well and good but unless I'm implementing it myself I don't need to care about the examples.
If you want to sell this to ordinary programmers you need to take another step down to the concrete level. Show two generic functions that take a category and show how they are useful for two different categories (heck, I think I can think of one myself: it should be easy to write a function that takes a type-aligned list [c a b, c b d, ... c y z] and combines them as a single c a z). If it's a useful abstraction then that really shouldn't be hard.
If you want to sell this to ordinary programmers you need to take another step down to the concrete level. Show two generic functions that take a category and show how they are useful for two different categories (heck, I think I can think of one myself: it should be easy to write a function that takes a type-aligned list [c a b, c b d, ... c y z] and combines them as a single c a z). If it's a useful abstraction then that really shouldn't be hard.