So just got past Moder, already dipped my feet into the plains biome along the way to get to Bonemass, and was excited to be able to use black metal to create armor and weapons. Turns out, you can only create weapons with it, and the next tier of armor requires more iron to craft it.
I can't tell you how happy I was when I thought I didn't have to delve into crypts and mine trash piles for iron anymore. Moving up to silver was so relieving as I wouldn't have to sit there smacking away mindlessly at mud. Granted silver also requires mining but it at least has interesting mechanics with the wish bone and it SEEMS that you get more silver per time spent mining. Its so annoying mining mud and getting another piece of leather scrap. Something about getting iron is just incredibly unsatisfying and boring, even compared to getting copper and tin. This is doubly true coming back to the crypts with black metal weapons and wolf armor and just plowing through the dungeon like its the meadows.
I think it would greatly benefit the progression of the game to create a way of getting iron besides the crypts. Possibly some sort of dungeon/tower in the plains that is difficult to go through but rewards much more iron for your time invested. Having to fight off hordes of fulings to get black metal is a fun and engaging way of getting resources for the next tier of weapons. I think it would be great to have the same sort of challenge combat wise for iron instead of having to play plumber in the crypts and shoveling crap for high end gear in an area 2 levels of gear behind where you are.