What had that quote got to do with Python3? In any case, Python is harder to embed and much slower.
You can embed Python, but making it safe to run untrusted code written by users will take enormous effort. Roblox is a platform for easily creating games and playing other people's games. They can't allow those games to pose a security risk to players' computers.
> Not sure how fast it needs to perform once embedded, apparently you know.
You're commenting this on a post that talks explicitly about wanting a faster interpreter than Lua 5.1. Nobody is switching from Lua to Python and getting better performance out of it.