It would be nice to have a hook for when the resource reloading finishes, to send changes to all connected players.
(The hook would also need to provide access to the Playermanager instance)

in Vanilla, this is done in Playermanager#onDataPacksReloaded(), where ex. crafting recipes are sent to all connected clients.

Implemented in #2265.

This hook should probably be fired when the data is first sent to a player too. Prior art can be found here.

This hook should probably be fired when the data is first sent to a player too.

Yes, totally forgot about that because I already had a mixin for it ^^

#363 has an event that covers this need.