Your argument is completely specious. Re-read that list. Assembly is a second language in the kernel already, and really it's multiple languages, one per supported ISA. Perl and Python scripts are used to generate data tables; there are multiple build-time languages. eBPF is evaluated at runtime; the kernel contains bytecode loaders, JIT compilers, and capability management for it. The kernel has already paid the initial cost of setting up a chimeric build process which evaluates many different languages at many different stages.