I didn't want to raise a non-issue, and I myself am not active in either mobile or embedded device environments. Personally, I would be happy to see the Jini codebase welcome Java 1.5+ code contributions.
I think in this case there's a great advantage that there is already a stable, production-quality, Java 1.4 version of Jini/River available. Maybe an advocate for 1.4 compatibility will step forward, and in that case, an option would be to add compatibility tests for clients and services written in 1.4 with those written in 1.5+. I'd also suggest that the project not worry about integrating Retrotranslator till we have one or more requests for it. It should be easy to tie into the main build process as a secondary deliverable in the future, but would just chew up resources at the moment. Anyway, didn't mean to stir the mixture, am personally (and as a current Jini user) interested in moving past 1.4. It's also very cool to hear from Jim Waldo to get some broader perspective on the topic. Perhaps the community can make a project-level statement like, "as of release X, River will begin to use Java 1.5 (or 6) APIs and language features." The main question I think will be which versions of the Java APIs River will develop and run tests against. Regards Patrick