Could update Font Awesome to V6 where is could be awesome to see theses new features.
Maybe you could add a feature for forum creators to set their icons pack of choices. Like Material or Fluent for example.
For Paid versions of Font Awesome, devs could buy themself without the needs to be implemented to Flarum. Just add a key activation tab and all was ready to go. Maybe sure the partnership with icons makers could be awesome to see it.