> Waiting for Cross-Platform standardized SIMD vector datatypes
These things are specific to CPU architectures, but other then that they’re cross-platform and de-facto standards set by Intel and ARM. Same source code builds with all mainstream compilers, regardless on the target OS.
> nonstandard extensions, libraries or home-baked solutions to run computations in parallel on many cores
OpenMP is not part of C++ standard, but it’s still a standard in the sense they have a complete specification: https://www.openmp.org/specifications/ Mainstream compilers are reasonably good at implementing these specs.
> Debugging cross-platform code using couts, cerrs and printfs
Debugging story is not great outside MSVC, but it’s not terrible either. When I needed that, gdb worked OK for me.
> Forced to use boost for even quite elementary operations on std::strings
I agree the ergonomics can be better, but I’m not using boost, and I see improvements, e.g. std::string_view in C++/17 helped.