One attains AA status by accumulating either elite-qualifying miles (EQM), elite-qualifying points (EQP) or elite-qualifying segments (EQS). I'll ignore the segments for now.

AA tiers of Gold (Oneworld Ruby) requires 25K EQM or EQP, Platinum (OW Sapphire) goes for 50K EQM/P, and Executive Platinum (OW Emerald) requires 100K EQM/P.

Most discount economy seats earn 1 EQM per mile but 0.5 EQP, some Y fare buckets earn 1/1, and full fare Y and all premium cabins including BA/QF premium economy earn 1/1.5. (In other words, a 1000 mile segment in PE/J/F will earn 1000 EQM but 1500 EQP.)

The challenges require you to accumulate 5000 EQP in 3 months for Gold/Ruby, or 10,000 EQP in three months for Plat/Sapphire. There isn't an EXP challenge (okay, once in a blue moon for very heavy hitters, but very rare.) Points must be earned on AA, BA, IB, JL, or QF metal (note, not CX, LA, or other Oneworld partners.) You also have to sign up for the challenge, $200 at this time of year. Once you meet the challenge, the status is granted until the end of February the year following, unless you start and end the challenge after July, in which case the status lasts until the second February. (I.e., start now, your status is good until February 2016.) AA uses a calendar year, not the anniversary of your qualifying, so to renew your status for 2016-2017 you'd have to fly/earn the appropriate number of points during calendar 2015.

Now, with your RTW itinerary, you'd hit 10,000 EQP on your first flight. Then, as Platinum, you'd receive a 100% redeemable mileage bonus on all AA, BA, QF, IB, LA, CX and most other Oneworld members' flights thereafter (including JNB-SYD, the flight on which you'd cross 10K EQP.)

Also with your RTW itinerary, a quick back-of-the-envelope calculation seems to suggest you'd come away with roughly 114,000 spendable AA miles at the end of the RTW, counting cabin bonuses (25% in J, 50% in F.) AA also requires 4 AA-numbered segments for renewal, which it sounds like you'd have anyway. Plus, depending on what month(s) the travel takes place, it looks very likely you'd also requalify for a second Plat year after the "challenge" year is done.

(I'm using old calculations that I committed to memory. With the US merger, I believe AA has changed some earning and qualification rules, so by all means visit the AA board before committing to this course.)

But it seems clear to me that AA might be a good option for you. Certainly I find its redemption options to be better than other Oneworld carriers - cheaper mileage requirements, fewer fuel fines... but of course things can change.

But with your big group traveling on a DONE6, it certainly sounds like it's a route worth investigating, and fast.