Had this feature on another server, and would love to see it here as well. It seemed to alleviate a lot of the house killing exploits that are common.
Adds a bookshelf inside your house. Clicking the bookshelf ports you down to a open footprint of your house underground. Standard house rules/laws apply. Only diff was marking runes inside was allowed. Was a staircase leading up, that would put you back infront of the bookshelf.