I will tend to agree with Chandra more.
Background
Fiori is created by Sam and his team to help SAP to build beautiful and user friendly applications. The set of Fiori controls, shell, tools, etc are the results of the effort to understand the popular SAP applications, think Mobile first, using Design Thinking to re-engineer and re-think how application should be developed.
Hence, one statement:
It is a set of guidelines and a set of reuse-able controls to help engineers (regardless of SAP employees or not) to build beautiful applications (regardless of enterprise or non enterprise application).
Moving Forwards
Fiori is evolving. The Fiori team is working with many partners on many projects and understand how to build beautiful application. They are learning new web technologies and tools; and using them as enablers to create beautiful and user friendly applications.
Disclaimer: I am not part of the Fiori team but I have friends in the team. And, worked with them in the past.
I still think that Sam Yen is the best person to provide answer to your question. I can ask him to chime in.
-D