I was thinking about this idea too.
It will even make more sense, if we are talking about realism and processes in vintage story.
I would say making iron stuff right now is pretty easy and it would be nice to have intermediate like:
copper -> bronze -> bog iron -> iron -> steel
Where bog iron should be a little bit better than regular iron , but can be found in lesser amounts. Regular iron ore should require 3rd tier instrument to obtain.
Also bog iron should be processed via bloomeries instead of regular iron. I believe, that we can cast iron in the future just because black coal can produce ~ up to 1.5k Celsius.
