Topic on Extension talk:NewUserActions

See phab:T118540 ("Allow adding pages to the watchlists of new accounts, either by default or during manual account creation") for details.

I think this might fit, into the idea behind this extension?

Yes, I imagine, as the extension has indeed the goal to allow onboarding workflows. For example, the first use case is the @Guillom's suggestion to allow to create an user page with a preloaded content for officewiki.