Statistically my house is not going to burn down.
And yet I have had fire insurance on all my homes for the past 40 years.
Similarly statistically if OP files N-400 now it, I-751, and the U.S. passport will all be approved and in hand before departing for Australia for the wedding. There is no question about that.
For OP, his brother’s wedding is a once in a life time thing. Missing it would be bad.
Dealing with an I-751 denial while abroad would be worse. Especially if USCIS informed CBP before it informed OP. Which USCIS is known to do. So that OP can be blind sided at the port of entry. And locked up until an immigration hearing.
These are all rare events. And yet they do happen.
The fire insurance here is:
* WoM to attempt to force I-751 approval before the wedding
* delay N-400 so that biometrics, RFEs, interview and/or oath are not scheduled.
Absent the wedding, I would file N-400.
I’ve contributed all I can, and I don’t wish to argue or bicker, so I won’t post more in this thread.