[Suggestion][Gameplay]Technology impeding & ways to get technologies

I've surfed through the forums and found a plenty of ideas for enhancing the tech-trees, but I've never stumbled upon a certain thing which I consider as important (if there was, I apologize), which is: I've never seen any suggestions about conditions impeding or completely prohibiting certain technologies from being researched. As far as I see the situation, there should be a way for certain conditions to completely block technologies from appearing in the tech-tree (perhaps until some more advanced condition are satisfied). Like, let us assume there is a certain technology which leads to three others (with 100% appearance rate), and researching one (or two, for that matter) prohibits two (one) others to appear in the tech-tree (at least for the time being).

Furthermore, why technologies are only acquired from research (that is, as far as I know from playing experience)? At least a possibility of acquiring technology from adventuring (completing quests and/or winning battles) is asking for itself to be brought into gameplay.