Ok, let's start with the easier one: New specialize books would be good to the game, which could enable us to use 3 resource, combat etc. books at the same time. I don't think that it would be OP.
The second one is way more trickier, and I haven't thought over it; it needs some balancing. Introducing boxes, which need more than 1 key to open them. These boxes would have a very very low drop rate, and they would require keys from shop and/or looted keys. They would drop continuously, not periodically, like the other boxes. Items inside would be all unknown, and I could not figure out what items could be there, I wass a bit tired this week, so it needs some further thinking. (Possibly schems/premium stuff only available from these boxes, or cheaper books from the store, etc.)