I like this theory a lot. It's almost like instead of trapping spren, ancient fabrial were created in tandem with it's own spren. See that's what spren really are, the cognitive representation of something that exists in the physical world. It's almost as if while creating the physical fabrial, the intent of what it was to accomplish or what it was to do was so strong that it's spren imprinted with that intent and became a willing part of the process. The modern process then becomes a real travesty and a perversion of the original way that spren relationships were supposed to work.