I think the idea is that if an API (or anything really) is using a flexible cryptographic model then it would be possible to string together any system for use in any cryptographic scheme.

For example: you could write the cryptographic equivalent of "if user deposits $100 into this bank account then allow them to redeem these crypto-currencies"

This would mean making systems broadly compatible. Anyone could envision new use-cases for pre-existing systems and be able to extend them without having to modify the existing system. But the challenge of this is (1) designing a simple, fast cryptographic stack (2) widespread adoption.