You are right, I have been lost my brain this evening a little bit.

I think without status, the LANPASS(LA), would be the best ffp for you. With the LANPASS, you get:

LHR -> NBO (BA/25%) -> JNB (surface) -> MRU (BA/25%) -> JNB (BA/25%) -> HKG (CX/100%) -> DEL (CX/100%) -> NRT (JO/70%) -> SIN (JL/70%) -> BNE (QF/100%) -> NOU (QF/100%) -> SYD (QF/100%) -> SCL (LA/100%) -> IPC (LA/100%) -> SCL (LA/100%) -> GIG (LA/100%) -> LHR (BA/25%)

Perhaps you will get also a status, but this you can average out, bye yourself. Edit: The costs(LANPASS use kilometers, not miles ) for a awardflight are also ok.
When you will have the chance, to make a Elite Challenge with AAdvantage, befor your RTW-Trip(nice route by the way ) start. Than AAdvantage is also a opportunity.

Edit2: When you want to have a Status for your RTW-Trip. Than will be the best way, to make a Elite Challenge with AAdvantage, befor RTW-Trip start..
Do you have any preferred oneworld Airline? It is also importand to know, for the time after the RTW( to get also 100% miles, for the flights after the rtw. )