I think if you were starting today, you would build the app as a set of backend APIs connected to an array of front ends (apps, mobile web, desktop web, 3rd par

I think if you were starting today, you would build the app as a set of backend APIs connected to an array of front ends (apps, mobile web, desktop web, 3rd party, etc). Building some or all of those backend APIs in Rust from day 1 would not be crazy, or less productive than any other language. I think differences in proficiency drive bigger differences in productivity than inherent language differences. So if you were starting today to build Facebook, using a language you are already effective with would matter more than which language you use (there are plenty of people out there for whom that could be Rust, or Haskell, or Ruby, or PHP, etc).