If you were to make it a 4x4 entity, could it then do 16 different ores? And then a 5x5 25 ores? I would think at least one of those should be able to handle the amount of ores, right?
At the very least, it should be possible to have different tiers of these deep mines, which could mine more ore faster, built from a deep mine and some other bits like iron and steel, and maybe even dynamically requiring bits from bobs and angels?
Or maybe it's fine as it is now, I should probably try the mod first :D