Posted this to give some feedback on the latest dev diary and to allow other people to do so.
Personally i really like the idea of a mirror realm as an endgame PvE type content in the way it is presented. I already think that the tactics school is a great part of the game but that once it has been completed the game feels like it is missing something.
More specific ideas:
1. You mention that once Heroes run out of energy or troops die you would have to leave the realm - again this is something i like - if you do this then please make it so that potions of any type cannot be used in the mirror realm or someone who has saved 100 or so potions has a massive advantage.
2. Some sort of cross server leader board would be fantastic
3. Somehow tie the mirror realm stuff to the current quests in the normal realm - there are lots of different ways to do this - i just like the idea of those quests having more meaning in the late game.