if you create a template yourself using ajax, then you don't do that.
if you create a template yourself using ajax, and you want the js to be loaded at each body reload: you load the js in body via the twig function registerTemplateScript()

Is this fixed or "no change required"?

So it's not possible to use $(document).ready() to load JS on every page?

yes it is

Version 3.0.3 released.