If you don't take investors' money, then it's theoretically feasible, but, in practice I've seen companies stuck with their Python/Ruby stack for 10 years or longer, always wanting to rewrite but never having the time. Microservice architecture helps (not that it's not a can of worms of its own), and these companies tend to write new functionalities in their desired language (such as Go or Scala) and deploy them as separate microservice. The old code remains in Python or Ruby though, and now they have a multilingual mess that is near-to-impossible to maintain for a small team. Why not start with a better language in the first place?