Brand new research tree

So lately, I have seen lots of suggestions of hospitals and special units like engineers. So instead of adding individual units like them, I say we introduce a brand new research tree not on units but passive bonuses. For example, if I research field hospitals, then all my units will heal faster or if I research engineers, attacking units won’t be impaired by fortifications as much. I have lots of ideas of passive effects. All of these passive effects can also be upgraded too.