Portable is a bit of a weird word here because for many of us with gray beards the word means architectures, kernels and systems, but I think in this context it tends to more mean "can run just as easily on my macbook as in a cloud container", but in practice the software isn't that portable, as Go isn't that portable - at least not in the context of vs. a niche C "portable network stack" that would build roughly anywhere that there's a working C toolchain, which is almost everywhere.
Constant security fixes for the kernel are a real pain in deployments unless you follow upstream kernels closely. If your business is in shipping Linux runtimes with a high packing density, you really need to find ways to minimize the exposed Linux surface area, or organize to be able to ship kernel upstream updates at an extremely high frequency (relative to normal infrastructure upgrade rates for kernels / mandatory reboots) (and I would not consider kexec safe in this kind of context, at all).
An alternative approach might be firecracker / microvms and so on, but those have their own tradeoffs too. The core point is that you want more than one layer between the host machines and the user code that wants to interact with Linux features.
