I see virtually nothing that would make this a "cash cow."
Whether it ends up being so is certainly up in the air, but I see all sorts of ways where it could be used as such. Reading the ToS, it becomes clear that the purpose is for data mining and more specifically targeted marketing than we are used to even today.
Through the use of RFID, Disney computers can track the moves you make very specifically. They can obviously already tell when and where you made a purchase, and what exactly you bought. Now they can also see what you looked at for a while, which displays you found interesting, what themes attract you, whether you drive or take their busses, if you were willing to wait in line with your daughter for 45 minutes to meet Ariel, whether you spend a lot of time at the pool or not, whether you like to walk around DTD (and which areas), which resorts you like to visit when NOT staying at them, and much, much more.
Combine it with the web now. What email offer will you get from the
Disney Store at home a few weeks after you return? Which hotel might you get a PIN code for? Today, all we have to do is Google disney, and watch what ads appear on other web pages you visit. Tomorrow, get your magic marketing band near a mickey watch display and see what targeted emails, texts, or coupon offers you get if you don't buy one - or heck, even if you do... While I don't believe it is built to anywhere near this complexity yet, I have little doubt that it is indeed a goal they are working toward.
The whole program is based on that; as others have posted before, FP+ and interactive cues are really just "side effects", and a way to get you to opt in. Eventually, we won't have a choice about that, because it will probably be in the ToS of purchasing a ticket. Magic Bands are meant to bring the use tech to bring demographics and psychographics in marketing to a whole new level.
My guess is that this is not about crowd management, problems with FP, or making guests' time more enjoyable, but about creating sales where there were not sales before. Whether through a targeted hotel and vacation offer, merchandise, restaurant offers, or just putting me in a place where these things exist, it is about increasing revenue and creating 'The Feed'.