Java didn't succeed in terms of running code in a web page but it has been wildly successful in regards to "write once, run everywhere". It is widely deployed and has been successful isolating code specific to a particular OS or platform.

While it's clear that Javascript has been successful in the "run code in a web page" sense, it's primary deployment target remains the web browser; even when it's marketed as a cross-platform solution it's often targeting something like Electron.

WebAssembly has its work cut out for it trying to succeed in both of these spaces. I think the project might enhance it's chances for success by remembering Java and its browser plugin rather than pretending they are the first.