By "Split Up", I mean "Which faction gets to do which zone"
From the preview of Chronicle 3, we see that Blizzard is trying to split raids, with Horde killing Magtheridon and Alliance killing Vashj. Then in Cata we have Horde raiding Bastion of Twilight and Alliance going Grim Batol.
So, why not apply it to zones?
My take: I will split it by Class, with different Class tackling different zones. The Race of the Class matters (Except Demon Hunters, because hail Lord Illidan), thus bringing faction into play.
Val'sharah: Night Elf Druid, Panda Monk, Worgen Priest (Alliance favored)
Stormheim: Orc Warrior, Human Death Knight (Both side duking it out, with Odyn passing popcorn in background)
Highmountain: Tauren Hunter, Undead Warlock (Horde favored, explains why HM Tauren joined the Horde because they didn't receive help from Alliance)
Azsuna: Gnome Mage, Dwarf Paladin, Demon Hunter (Alliance favored, Farondis joining Night Elf to fight against Azshara)
Suramar: Blood Elf Rogue, Goblin Shaman at start, other classes join in later as Suramar campaign progresses (Horde favored, Nightborne joins Horde because it's Horde who helped the resistance survive their toughest period)
Broken Shore: Everyone
These are my takes, how will you split Broken Isle?