Probably better for BRICS countries to consider contributing to something different.

Realistically there's no feasible way for the US to block access to use the kernel, and even a soft fork of it will be laughably easy for glowies to exploit. There are a bunch of promising kernels that could be well suited for China and Russia's push towards RISC and ARM independence, whereas in Linux they'd be tasked with maintaining drivers and other systems that are a massive security vulnerability if you don't have total control over them.

I'd honestly even consider it a good idea for Russia to get the FSF to fight this considering it's a blatant violation of the GPL. Even if the president can just say whatever they like, at least you can make it embarrassing and expensive for the chauvinists gloating at the labour they exploited for years.