ETA for OpenMP 4 features says OpenMP 4.5 features are coming in 2018. Can you provide more details? A table might help.

I currently find that OpenMP target code will compile and run on a CPU with 17.4 on Mac, but presumably this is a no-op implementation. It does not work when I add collapse(2).

On the other hand, taskloop does not work in 17.4, which is consistent with the aforementioned summary.

A matrix of features and OS+HW support would really help users. Thanks.

The OpenMP 4.5 support comes in the PGI LLVM back end compilers,
one of two compilers coming in 2018, where the proprietary PGI x86-64
back end compilers will be available along with
LLVM back end. The LLVM version will have OpenMP 4.5 support.