I don't think that GH code is easily accessible, with rate limiting and TOS forbidding it. GPT is an open model (for the most part), but its training cost is in the order of tens of millions of $

I can think of no one but a handful of companies being able to compete there. And they won't be ok with extending a Microsoft IDE, nor breaking GitHub TOS.

When you start competing on R&D costs the game changes.

There's always the chance that training costs will significantly decrease. But even at an order of magnitude less (ie. tens of Ks) it's still beyond reach for open projects and indie devs