One of the best retrofitting effort there is is Java's Loom IMHO. Instead of trying to solve the IO bottleneck on a few threads with async, it just reduces the

One of the best retrofitting effort there is is Java's Loom IMHO. Instead of trying to solve the IO bottleneck on a few threads with async, it just reduces the Thread footprint and allows you to have millions of them. Good'ol Tomcat is going to massively improve its IO concurrency overnight with just a simple `Thread.builder().virtual().factory()`.