If I remember right though, the smallest devices running Java (comparable to the AVR devices in specs) were mostly designed at the hardware level to run Java, s

If I remember right though, the smallest devices running Java (comparable to the AVR devices in specs) were mostly designed at the hardware level to run Java, so there were lots of considerations made that wont be true for an AVR microcontroller that has a first-class C toolchain. Additionally, the Java Card specification was a pretty cut down version of Java that didn't have the same "Not _yet_ supported" feature list here.