If pitches are essentially and fundamentally like colors and phonemes, and this explanation of how colors and phonemes are learned is reasonable, then absolute pitch learned by the same processes and mechanisms would demand the same embodiments, namely, environmental objects and melody-words. Perhaps the reason these types of sounds have been considered is that they are indeed, obviously, the sounds you'd want to use-- but they've never worked to teach absolute pitch because training systems have used them inappropriately. If I'm going to develop a training system that works, I need to figure out how to use environmental pitches and melodies in a way that has never been thought of before.
I am taking another stab in the dark here. It seems to me that if environmental sounds and melodies were part of the process of acquiring AP then the function of each pitch is quite artificial and arbitrary. Therefore the function of the pitches in any training system would have to be invented seeing that any real function is not that apparent. The system would have to invent functions that were novel enough to be significant to adult (or other) learners - something like part of a code or series of codes for instance. Another may be to make the pitches correspond to keys that unlock doors or secrets in a game or something with appropriate rewards attached to unlocking and also with repetition of key codes throughout the game.
I read somewhere about the system, used in Japan, of telling people what train stop they are at. It used melodies as signals as a kind of background cue. Kind of like web pages that are designed with particular colour backgrounds to coincide with topics of interest within the site so that the surfer is being guided along the right track almost without thinking about it in any overt kind of way. This may have some kind of use in ear training systems too I'm thinking. Maybe as part of a game there could be environmental signals happening at random at various stages, maybe a bird in a tree whistles a tune (the tune could imbed a note that is being worked on the same way that APA does) as a character is walking along, or a train whistle blows or whatever, then this is incorporated into the clues to unlock specific codes using specific pitches.