16 segments forces some prioritizing, especially trying to visit interesting non-hubs on 6 continents. 50K mileage limit is no problem, even moreso only counting stopover to stopover distance. Award Availability to Australia can be difficult so you might plan around that(forget JFK/LAX-SYD/MEL, but HNL-SYD, non-SYD/MEL australia, & cathay routes sometimes open). Lan Chile releases just 1 first class award seat per flight, but you want 2. Brasil requires visas applied for in advance.

You can get away with really crazy routings backtracking repeatedly through continents since normal RTW rules do not apply -- just one stopover and two transits per city. You might not take advantage of that too much since longhaul flying is exhausting even in first class, depends on what your partner can stomach.

To extend segment count, use cheap awards within a continent (use open jaws and/or stopovers), or buy segments seperately where cheap (like LIM-CUZ-LIM, and many Australia flights). Another possibility is interesting one-way overland trips, saving you from backtracking and saving several segments.

JFK-EZE-LHR-CPT//JNB-SYD-HKG-JFK 7 segments

a few easy add-on ideas
EZE-IGU Iguazu falls, not oneworld yet (lan argentina someday?)
LIM-CUZ Cuzco Peru: for machu piccu-- 7 day stay is good for 5 day hike
SCL try Vina del Mar nearby. Skiing nearby too.
SCL-PMC Puerto Montt: so pretty and easy, short visit ok, try lake boat trip
SCL-PUQ awesome hiking trip torres del pines, penguins
SYD Many fantastic walking trips reachable via train&ferry
SYD-OOL If you don't like the gold coast something is very wrong with you
SYD-CHC Christchurch,NZ: southern scenic route driving is awesome
SYD-DRW Darwin late may/june good, exotic&rough 3-5 day hiking trips
SYD-CNS Cairns fantastic super easy tourist spot, great scuba too. Go go go
JNB-LVI Livingstone for victoria falls (Zambia side, avoiding zimbabwe)
HKG-BKK Bangkok: smog traffic humidity, great place anyway. Cheap&Fun to shop.
HKG-NRT//KIX-HKG land in one airport, leave from another, train between.
Hawaii Ahhh, you know you want to
Costa Rica Well setup for tourists, nice things to see
LHR-PRG/VIE/BUD Land in one, leave from another, train between.
LHR-LCA/ATH I luv cyprus & greek islands