Just because there may be better tools now, should they scrap their working code that earned their fortune?
In terms of what Instagram should do now, I'd say they should do what Facebook did: introduce thrift or similar, gradually move business logic into backend services written in more suitable languages, leaving the Python to eventually become just a thin web frontend. Retrofitting types onto code involves a lot of the same effort as rewriting it into a better language, and the rewards for the latter are higher, IME.
We still have to work with the world as it exists. Not as it should be or will be. And even with the crop of modern languages, its often still faster to start with less optimal languages and fix shit in the 1/10 chance you're actually successful.
Haskell remains impractical for many use cases, it is not used much outside of academia, it's not documented to be used outside of academia, and it didn't even have a working package manager until a few years ago.
Not sure why the negative vibes toward this comment, I think it's fairly sensible (of course, this is a very subjective subject).