Openfire is already bundled with Java 7. Afaik, dropping Java 5 / 6 support only means, we can start using Java 7 APIs and language features.
The more I think about it, it's probably better to drop the Java 5/6 support in 3.10 and maybe introduce a new buildsystem. Then think about what we can do now with Java 7, and discuss things like DI, StaX, Testing for 4.0 as those things probably require some major restructuring and API changes.