Redrawing the ROM map

There are several things people want to expand, and the reason I make this topic is to discuss what makes sense when trying to put together an expanded ROM.

As we all seem to agree that it would be a good idea to make some kind of open project to optimize and organize, there are a few ideas and observations I want to put out there before I forget.
Mon
First: Map expansion. I know it can be done, but I have no idea how to even begin there. I'm sure whatever kind of map data can be expanded would need a dedicated editor to handle it.

Second: Event expansion. The existing events in vanilla take up almost 3 whole banks. Moving the events would be a very difficult thing to do, as they are loaded from so many places. What I would suggest is to move anything out of CC and CD that are not events. The existing event engine can easily handle going into a 4th bank (since 3 is not a power of 2, this should be obvious). I believe CD holds (among other things) the dialogue pointers... which would be an easy thing to move.

Third: Code expansion (specifically the C1 bank). I think one additional bank of code would be all that is needed, although code can go anywhere easily enough with long jumps, provided you can find room for a function to pass the options through.

Fifth: Monster expansion. I don't know where it is without looking at the ROM Map, but I believe that adding monsters to at least 512 would be fairly easy in most respects. The monster data itself can be placed in a larger area. The sprites would probably be the hardest thing, and I'm sure that can be done as well. AI would probably need a new bank, but that's just one block of data and its pointers, so not too difficult (note that, without some code changes, monster AI scripts above 0x8000 in their bank will not trigger their counter-attack scripts properly, so a hack is needed there).