Oh man, just think of the possibilities for that. Mostly, an uncompressed map format, totally unique rooms, just overall more control. Considering how large the main map is, I would say 256 rooms is sufficient. Each room could contain it's own room header that's static and easily edited, and the map itself could just be a simple arrangment of those rooms. Now let's see if I can do the math... Okay the map has 24x24 spaces, which is 576 spaces, each room containing 112 tiles. 112 x 256 is 28672 tiles which is 7000 in hex, which is over 1 banks worth of information. However, that also leaves room for a shadow bank that could contain altered room states. 512 rooms is really too many rooms since otherwise there would be no point in having a map. Let's cap it 256 rooms, but give each room a shadow bank for altered room states. That would take 4 banks, and it could be organized that from 00 to 7F could be in one bank, and 80 to FF could be in the second, and the altered states could be altered from the first in the other 2 banks.
The header would contain the same information as before except that there would be less flags used to determine length. Instead of a pointer, each room could just have allocated level data affixed to it, so room 00 would stat at one address, and room 01 would be that + 112, and so forth. Flags would exist to alter room state, and perhaps an event number, and it would tell the game to load from the secondary banks. Each room would be given an item and monster data as well as any other effects. Gone could be the room directions, and instead it could act as a free roaming map like in Zelda, and perhaps the warps could be retooled to have one seperate tile for each direction, as well as what key unlocks it in the room header.