Saving player specific data should still be a real mess. A save system would be another necessary feature.

I really like the idea... basicaly also on normal game modes... I could imagine that with this technique the map size can be extended to nearly unlimited.
When I think about the transition from AOE2 to AOE3 one thing what bugged me a lot was the tiny maps that were a restriction due to the fancy 3D Graphics...
So I could imaging big production lines... one Map to farm wood, one for ore etc... and between the maps you travel with a train that simply drives in the Z-Direction out of the Map and then spawns again in the target map... also this could be used so to transport materials between maps...
All in all this doesn't sound too hard... though as Ringwaul (not sure) mentioned somewhere else that we need something to save the state of a complete map... I only see a restriction then with the usage of the RAM but nowadays this shouldn't be that issue anymore...

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