Higher difficulty at a razonable level (I think)

Make some kind of block or object that you can obtain in the temples and importan structures (like desert temple, jungle temple, ancient city, mansion, sea temple and bastion). You gotta put these items on the portal (besides the eyes of ender) to get access to the end dimension. Maybe put them like blocks at the corners or edges of the portal, or just put them directly into the portal blocks just like the eyes of ender. This would make better the exploration's experience and the importance of some structures, also, this would higher the difficulty of the game at a razonable level