Thanks for this thoroughly practical advice -- evangelizing types inside Stripe must have been quite the journey! Been following since Dmytro and Paul's talk @ strangeloop.
Interestingly enough, I don't recall there ever being much pushback against static types at Stripe. The "evangelizing" work was more organizational: convincing people that yes, it is possible to build a production-ready type checker in 6-9 months[1], and then staff a team long term to continue improving it. I was at Stripe during that time, but on a different team, so I can't speak too much to the process.
Luckily I think Stripe is a well-functioning org with smart and reasonable leaders—much easier to present that case than e.g., trying to win debates on static vs dynamic typing on the internet!
