I was aware of, and practising, timeless decision theory before ever stumbling across Lesswrong, and, while I know this may just be the "typical mind fallacy" I would be surprised if only 0.1% of people had similar thoughts.

Sure, I didn't call it TDT, because that is a piece of jargon only present in this community, but the basic principle is certainly not unique, or unknown, and I would expect that even many who don't undestand it would use it subconsciously.