I've always felt that it's better to have concurrency properties declared as part of the type, guided by C++ atomic<>, and VarHandle was a step away from that (towards concurrency "assembly language"). It's more difficult in Java where there are no zero-cost user abstractions (yet!).
I'm worried about a hardware dependent performance cliff when the size of an object grows beyond some word size and locks need to be used. Java still needs that revised memory model, but it's very difficult to get right.
