MKA is suppose to be the final chapter of MK as we know it. Boon and co will be starting fresh on the next gen systems with new characters and storylines. So I propose this stage as a tribute to MK's rich history...
A museum or shrine of some sort that contains many relics and references to the past. The walls are adorned with murals of famous past MK battles. There are relics encased for public display that actually belonged to past MK kombatants. For example you can see Sub Zero's and Shao Kahn's masks on display. There will also be encased weapons such as Kahn's war hammer, scorpion's spear, and Shinnok's amulet. You may even see a preserved shadow priest as an exhibit.
Now here's the kicker - when fighting on this BG, MK8 kombatants will be able to break the cases and use these relics to aid them in their battle. No doubt, this stage will also harbor many secrets and possibly a hidden character that survived the ages.