Not OP here, but it did disappear from the frontpage. I was still pondering about it and left this tab open... frankly I can't think of a good use case for it besides making legacy java apps available via browser. For gaming, I'd probably still use Unity or other game engines. For app development, I probably not gonna develop on Java 11 again which the support gonna be ending in 2026. I'm impressed by this project though.
The legacy use case is indeed very important, but there are many other opportunities that can come from using Java libraries as part of Web apps.
CheerpJ provide "Library mode": an API to natively interact with Java objects from JavaScript: https://cheerpj.com/docs/guides/library-mode
CheerpJ also support Java 17 (currently in preview) and LTS parity is scheduled for next year.
I use CheerpJ to do new development that is spectacularly cross-platform, runs native on all the major platforms and everywhere else in the browser with a single code base. I don't think there are too many alternatives for that and I suspect Java + CheerpJ is one of the best.
Being able to access the entirety of the JVM ecosystem of libraries from JS without glue code is kind of insane.