Thanks for the feedback. I never made any point regarding type-safety so I'm just going to gloss over that. I have no issues with static typing.

Also, I did not mean to say that you should not move to something that inherently runs faster, that would be perverse. However if I have a system written in a language that already works I would probably start by looking at algorithms and architecture before pulling the New Language card.

Once you have a set of interoperating services then re-evaluate which, if any, individual services are my performance bottlenecks that could benefit from the effort of re-implementation in a new language.

The really interesting discussion of course would be one that included engineers from Twitter and their recall about what happened.

I have been in enough design meetings to know that their strategy didn't emerge fully formed from the mouth of one person.