https://github.com/bhauman/lein-figwheel#preventing-and-forcing-file-reloads

so, you suggest having a NS (in env/dev/cljs or something) that invokes my :on-jsload side-effects and tag it with ^:figwheel-always? and having a separate one per module?

Just put together an example Repo that shows code-splitting in use with figwheel here: https://github.com/clojure-examples/code-splitting-example