Yes it is. Stripe can do this with three (badass) engineers while the hundreds of other engineers continue to build their applications in Ruby. Stripe's Ruby

Yes it is. Stripe can do this with three (badass) engineers while the hundreds of other engineers continue to build their applications in Ruby. Stripe's Ruby code base is far larger than their Scala codebase, with each being used for the types of uses that play to their strengths. Rewriting millions of lines of Ruby into another language would more or less involve pausing all application development for one to two years, which simply is not feasible. This way, a small team of skilled engineers make this typer work, and guide its general adoption, getting the codebase well typed over the course of years, all the while Stripe continues to grow its product suite and further conquer the world of e-commerce. Twitter did a huge Scala rewrite. There are many lessons to be taken from their lack of product velocity while doing so that the Stripe team took onboard when making this decision.