I was on a team with a similar timeline with C++ (4 year). All the language and toolchain difficulties came after shipping. Meeting new customer needs meant shifting from greenfield to brownfield engineering. We were chasing down strange platform and provider behaviors. Adding features while maintaining performance and correctness, meant relying on knowledge of tools available in the broader community. Solutions for build issues came through a combination of in-house effort and industry partners with related experience. Having two stable compilers (gcc and clang) was super helpful.