How about Hercules and Iolaus (from the Legendary Journeys of Hercules); and Xena and Gabrielle (from Xena tv show). Probably would need Hercules to be the size of a Destiny Fallen Captain, Xena CoD size, and Iolaus and Gabrielle Halo/TMNT size.
I believe these might have been mentioned before, but not for the MCX Heroes line. At least then we'd have some ancient Greek figures, pre-troian war era that is. Then maybe expand into a full line with Cyclopses, Hydras, Centaurs, and so many more. Pretty sure it was because of "the Legendary Journeys of Hercules" that got me interested in ancient Greek history.