I'm still learn about JIT but what happen if we JIT everything as in every single line of a Ruby app? Will it be way faster? So we don't have to wait for the JIT to compile during production?
This is called AOT ;^)
You may want to look into TruffleRuby from Graal, with the "--native" flag. Particularly some of the writings Chris Seaton (project lead/founder) from Shopify has about it: