Yes, Java and C# will become obsolete, but for a different reason — they’re OOP languages, which results in a lot of unnecessary complexity. Its focus on mutable state results in unreliable software. OOP wasn’t made for concurrency, which is extremely important in the modern day and age.

Functional programming solves most of the issues of older languages. It solves most of the problems caused by OOP. And FP really is the future.