Not if it turns out to be usable and have a significant impact on the performance. You need to realize that at the scale Youtube works, even a small performance boost translates to huge savings in server cost.

So the worst case here is if they never improve this past their own needs (which is a pretty limited subset). But if it's successful for them, and it's opensource, I could very easily see other people who run heavy stuff on Python contributing to it and helping it grow.

That's the thing with opensource, even if Google doesn't actively work on it, others can (if it has actual value and is useful to people).