@strategyonly
Good idea, I added a link to the main page in my signature. It seems like a concise place to cross-link without much clutter.
@Freezer-TPF-
Thank you! Engineering was sort of a "gut feeling," it seems like a good place to have a production upgrade. Here's my reasoning:
Too early, and a change to mines might throw off the progression of the game too far from what the developers intended. Mines are a very core fundamental aspect of the game, so we've gotta be cautious when changing them.
Engineering unifies several different military techs on the bottom of the tech tree, making a game opener there an interesting choice now when stacked up alongside the Stonehenge/Great Library to Civil Service game opener (food upgrade, two eras, and the valuable Pikeman). It's not too high up either, so it's feasible to work to in early game. Lumbermills were already at Engineering too, and that tech is otherwise a bit empty, with just forts. Engineering is also in a chain of several other improvement upgrades: mine/chop, quarry/clear, bridges, lumbermills, road speed.