Wouldn't Java 1.0 code still work in Java $LATEST even with modules? As i understand it the question was about keeping stuff working, not refusing to add new stuff.
1.1 is what would still work. There was not much Java 1 code in existence.
Java 1.4 to 5 was annoying and the last release to introduce a lot of source code in compatibility. Which was sometime in 2004. Modules is mostly figuring out what switches to set on startup, not so much refuses to work.