I can see checked exceptions being a good option for a pre-Java8 world, but they interact horribly with functional interfaces, which are fundamental to a bunch

I can see checked exceptions being a good option for a pre-Java8 world, but they interact horribly with functional interfaces, which are fundamental to a bunch of other newer Java features. A lot of those are almost philosophical differences, though. A Java feature that is unambiguously bad, but probably impossible to remove, is the different equality semantics between atomic types and their boxed versions.