They could have overshadowed the documents web. No need to extend text/html, let user agent run application/flash. There would be causalities - accessibility,

They could have overshadowed the documents web. No need to extend text/html, let user agent run application/flash. There would be causalities - accessibility, responsive design, ad block (cosmetic and network), personalization (stylus). Yet with still unmatched creativity, maybe with stronger case against native applications (like today fuchsia). World would be different and we would never know exactly how.