Building a Java Applet and Flash Player SHIM in JS

How hard would it be to build a JS-based Java Applet and/or Flash Player SHIM in the browser? I see lots of archival attempts on the internet such as the Wayback Machine, but much of the interactive content from the early days of the web is now inaccessible to many as we shift away from native plugins to web standards. With modern JS VMs, it seems as though we ought to be able to support JS-based Flash and Java runtimes inside the browser. Are there any projects in place to make this a reality?