GTK2->GTK3 was a major leap. For something like a GUI toolkit, changes and advancements are inevitable. A GTK4 port would be much less difficult, as the developer-facing changes are an order of magnitude smaller.
You should know, Shepherd is extremely power. Because you do everything in scheme, you can use regular programming constructs and hack on it with a REPL. It's written in Scheme (Guile) by itself, the same Scheme used for Guix.
oh, you haven't seen nothing yet. you know the lisp-y, hackable goodness you get in emacs? what if an init system was that hackable, and configured with a lisp? go give GNU shepherd a try.
main character