Query : The Jambiya/Keris Effect
 

Just for fun:
Could the spread of Islam through Indonesia, Malaya and the Philippines have had an influence on the wearing of the keris beyond the borders of Jawa/Bali ?

I would say undoubtedly so.

There seems to be little doubt that the original spread was through Majapahit influence, but since the keris was the prerogative of the elites in Hindu-Jawa, it would only have spread to the elites in the rest of SE Asia.

With Islam it became an icon of the people, rather than the elites, and there was continual contact through trade between Jawa/Bali and other polities in SE Asia.

I believe that the spread of Islam in SE Asia had as a side effect, the spread of the keris.