Pretty much 1024x1024x256 maps.
Old small maps could be loaded by adding an option to load large medium and small maps.
medium maps current size.
small maps 256x256x64 or 128x128x64
The reason this is being suggested is that most of the maps made currently will get demolished, and it will be completely chaotic running some of the maps that are made currently. so, increase the size of maps to accomodate them.