No people do this all the time - a few years ago I read an article where the secret sauce was writing everything in lisp (good luck hiring for that). Goldman Sachs does a lot of work in erlang but mostly to limit turnover on the dev side - try getting a job if all you have on your resume is years of working with a language nobody else uses, you can do it but it’s going to take a lot more effort on your part. I came across a place in Austin once where they did all their work in a toy language the manager wrote in college (greatest job security move ever). Java was supposed to be the solution to every problem, so you could migrate seamlessly between the single platforms in use at most companies. I remember lots of articles were switching to Java is what made the volume go to eleven for company X. More recently I see a lot of articles are Golang is how company X is keeping ahead if their peers. I’m sure I’m a few more years there will be something else.