This is what I'd consider doing if I was a small AI lab. Don't try to build a frontier LLM that beats all benchmarks. Try to make the world's best LLM at one programming language. Create your RL pipeline that puts all your resources into making the LLM the best at that language. Even better if there's a dearth of human-created training data on Github, since all your competitors will be bad at it. Google somewhat did…
I'm not saying this is a bad idea, but it does sound like a rather risky prospect. You're basically proposing a bet against the ability of LLMs to generalize across programming languages, and to embed concepts at a deeper level than the syntax. Many people do think this, but I'm not sure many of them are running AI labs.
https://arxiv.org/abs/2407.21783
See figure 8.