This post in no critique. I find the new update in metal industry very healthy, rational, and big thanks to devs here.
On the idea side, I find reasonable to see 'aka' the bone/stone (no metal), soft metal, and hard metal 'ages' a bit more pronounced and stretched even more in time. I believe that this could be accomplished in few way: increasing LP cost buying skills AND introducing a reasonable RNG event to enable the access to another skill (to make the game less deterministic). The ability to transit into or learn other skills could be dependent on INT x LORE x the ability type (like masonry for metal, farming for farming and gardening, etc.).
Thanks.