I responded to you before I had my coffee, so I didn't realize that you are one of the admins for aussie.zone.
I will tell you what: I am 100% sure that I can write a service that can work as a bulk message relay and I'm equally sure that I can modify Fediverser's code to make it able to ingest data from the relay. If you want to join Lemmy's Matrix Room, we can chat to see how to best solve this.
There would be no customization of Lemmy itself. You'd only have to add a sidecar service.
If you don't want to do it, fine, no one can force you to. But then perhaps it would be nice to be transparent with your users and tell them that the delay in federation can be avoided.