Echo likes, a lot. Especially the aspect of how they are not hollow armor, but rather armor that wears people... or pieces of them, at least. I can really imagine a bunch of Knights holding down a captured victim, and forcibly dressing him up in the armor, then letting him rise as a complete knight.
Really good stuff. A great corner stone to a plot or a even better yet an unavoidable red herring where these to be worked into plot. The reason I suggest these would make great red herrings, is because for all their fluff, chrome and power, they are not villains, at best they are victims and worst they are forces of nature at this point (or slave to their nature). Ultimately, unless you were develop the roles of the gods or the lost priests order, these are not roleplaying tools. These knights are tactical challenges or puzzles, but their is nothing innately character driving or developing in this for the PCs that will interact with them.