I'm currently favoring Randino's plan as well, because it has a very synergistic effect between Stewardship Ministry + Australia + Psionic Institute. We're going to need a lot of funding and economic investment to actually develop Australia once it's conquered, not to mention the artificial sakuradite production we can leverage by extracting exotic materials (eezo), plus all the trade deals we can make to facilitate that.
The other alternative plan I'm toying with is trying to get "A Formal Non-Aggression Treaty & Defensive Treaty Between the Federation & Britannia" to shake-up the geopolitical board entirely if that provides a good opportunity. Something like:
[ ] Plan: World Unification
-[ ] The Empress' Hand in Marriage.
--[ ] As First Husband.
-[ ] A Place in Her Administration.
--[ ] Piety
-[ ] A Formal Non-Aggression Treaty & Defensive Treaty Between the Federation & Britannia.
-[ ] The Taklamakan Desert Research Grant & Small Political/Trade Favors (For Charles).
This would let us open a Psionic Research Institue as part of the Ministry, marry Lihua, and cement an alliance between Britannia + China with a formal treaty alongside a bunch of political/economic deals for mutual benefits. We can then conquer Australia using the political capital earned from the alliance to gather a coalition of military forces in a joint operation rather than relying solely on China's fleets, which isn't a good PR look.
Remember we've got that meeting with the Governors of Area 8/9 coming up? Plus we just got the Crowns, and Indonesia would love to join in against piracy, etc.
I would be more confident if we had completed the Bodyguards Intrigue action.
On the other hand there is the fact that she is the heiress of a Britannian Duke. Would they try something during a visit?
Kallen doesn't want to bring Bodyguards with her, and if she's fussed over her safety too much Lelouch suspects she would just cancel the trip, like the update said. Slayer clarified the main danger is political/bureaucratic, not a physical threat to Kallen or her family, unless it's a worst case scenario, in which case our shinobi and Kallen are trained and capable of exfiltrating themselves.
It's a win-win scenario whichever way Kallen's trip ends up going - nothing happens and Kallen is able to relax, or something happens and we can intervene in Japan's turmoil while Kallen becomes even more loyal to us after her last ties to Japan are broken.