IMHO - you should learn Common Lisp - it solved the problems described in the talk (Nim can't redefine types on the fly) decades ago. In Common Lisp you can redefine _everything_ on the fly. You can change types (classes) in a running system and objects in memory that have the layout of the old class get upgraded automatically when they are used. Programming with Common Lisp in Slime/emacs is an amazing experience that will spoil you for other languages.