it took them 2 years.
For me at least the overworld is the least important aspect in a 'mon game. I have a bias from the time playing shoddy and PO though. Nether the less, when you think about it the overworld has 3 main parts; routes, towns, and caves.
just to break that down more in a very course sense,
towns include: shops, npc encounters(gyms), dialog with npcs routes: random encounters on hot tiles, npc encounters caves: random encounters on all tiles, npc encounters, puzzles
I haven’t played ardventure yet but from what I’ve read about the battle mechanics and monster count some aspect of the game would have to be reduced to fit the more complicated battle mechanics. I feel like splitting the overworld into separate games and using a shared EEPROM file like how @filmote did with loderunner would be the best option vs trying to cram the whole game into 1 hex and make a bunch of compromises on what to include. Even if that ends up being a hassle to have to flash your arduboy. At the same time though old games would require you to swap disks which is pretty equivalent to this
Just as a mental example there could be perhaps 4 files. 1: Starting town and a route. 2: route and a gym. 3: cave/dungeon , final 4. 4: battle tower.
Another potential, File 1, all routes, file 2 all towns, file 3 all caves. Use a flag in EEPROM to determine where you are.
//numbers are the level sequence routes towns caves 1 2 3 4 5 6
Granted this would be more tedious regarding having to flash more often.
Keeping the only 2 area types to a file or just one like the second example would let you save memory by not needing all the different mechanics at all times. Only files with caves would need the puzzle mechanics, only files with towns need a shop mechanic, etc. Another advantage of this kind of layout would be other people being able to create caves as challenges or various other tower of battles ect. Unfortunately my mental gymnastics do not reflect producing anything of substance in reality.
Also as a side note, circuit dude could easily be an easter egg sudo legendary. See: rotom. Using characters from other ardu games as legendaries or NPC opponents would be a nice community spin. (the arduventure character could be the final boss or a secret boss etc)