Ruins in the Deep Dark rarely having Ender Chests as points of interest

It fits the lore (that we know of) of the Deep Dark somehow being connected to the End dimension, and also ties into progression; there's no easy way to learn about Ender Chests in-game yet, besides in End Cities. 

I think the best part about this idea is that Ender Chests glow and can be seen from afar. If the player sees one, they could be tempted to either open it or break it, which is something the Warden could hear and investigate. Ender Chests would serve as checkpoints, too, to allow players to either restock or store any valuables before going further, but being rare occurences, you wouldn't be garanteed to find one, either.