I like certain aspects of it ... like Necromancy (super army magic) being locked until defeating an ancient Necromancer/Bonelord, and super-library techs possibly being unlocked (or made cheaper) by holding the Fallen Library. In fact, it makes more since for Education based techs to be X% cheaper as long as you occupy the Fallen Library (30% cheaper?)

It'd be kinda neat for Cave lairs/dungeons to have a chance of containing some rare mineral, and so there is possibly a slim chance of X dungeon uncovering a cache of shiny metal ... and that either unlocks mithril working tech or makes it cheaper to build (by 20%) .... not entirely certain about that however. Also, It brings up the question of at what point do the developers want resources to be revealed? WIll they be revealed one relevant tech Prior to the one that Makes use of the resource? WIll they be revealed at the tech that makes use of the resource? or Will they ALWAYS be visible (or findable in dungeons/caves)?

Anyways, I also agree that physical requirements not be for "main" techs, but perhaps a natural presence of fish could make fishing tech slightly cheaper, and natural presence of wheat could make farming tech slightly cheaper, ect. (over-abundance of BlackSmiths could make weapons tech slightly cheaper, over-abundance of armorers could make armor techs slightly cheaper)

yea, you could move troops through caves in the mountains

although How one will find these caves/ navigate them/ and how many of which faction can fit through the caves will be another matter. I ask this because I find it hard to do diplomacy if their merchants and statesmen have no passage into the empire. (ergo tunnel roads through the mountains ... but that then negates "impassable mountains" ... unless you have a prince or two on the outside of your cities doing all the negotiation, but then that means no "trade"