Unexpected productivity boost of Rust

I feel like this is exaggerated. If you spent a couple days building a POC in python and found that it was useful then you can spend a couple days re-building it in a better language. You already know what you're making, probably have a decent plan for how to implement it, should be simple and straight forward to replicate it.

It's not exaggerated. You can spend a couple of days rebuilding it in a better language (and I have done that!), but what actually happens is people want new features far more than they want you to rebuild it in a better language. So in most cases it gradually grows and gradually gets more unmanageable and it gradually becomes more difficult to justify a rewrite. There's never a solid point where you have to do a rewrite so it grows and grows until you really really wish that you had but it's also way way too late.

Happens all the time in my experience. It goes so far that big companies like Facebook, Google and Dropbox have all ended up writing their own Python/PHP runtimes or even entirely new languages like Hack and Google's new C++ thing rather than rewrite, because rewrites become impossible very quickly.

That's why - despite people saying language doesn't matter - it is very important to pick the right language from the start (if you can).

That's fair. I wasn't really defending the idea of using python for prototyping. Personally I'd just start with C# for pretty much any project and try to do it right from the beginning.

I suppose most of my point was that in the case described one should jump to the rewrite sooner rather than later, to avoid the situation you describe.