Here's a simple spoiler about the future arena maps. Those are hardcoded in the game with a complete list of test maps.
Code:
PvP_caOut_Arena_01
PvP_Maze_Arena_01
PvP_Octagon_Arena_01
PvP_Stairs_Arena_01
PvP_Crypt_Arena_01
Here are the other test/hardcoded maps for those who are interested:
Code:
Axe Holodeck
Axe FlatWorld
Limbo
MarkerSetTool (World)
lightmapper_placeholder_3
PVP_Test_Arena_01
PVP_Test_Arena_02
Axe StartWorld
BlizzCon StartWorld
Tod_LoadScreen
Scene Edit Tool (World)
BattleNet_MainScreen
Axe GizmoWorld
Axe HolodeckBlack
I'm not sure if any of those are accessible, I'm currently working on the reversing of the system handling all SNOs so I guess when I have something working I will be able to test those. But since it seems like files aren't in the MPQs, I wouldn't think so.