One of the most amazing things to me about the whole Disney company is how they collect data. They know exactly what is going on, and everything has a purpose (for better or for worse).
When Disney is referring to changes they've made "due to guest demand" what they really mean is "due to our very detailed research". This whole idea about RFID tags relating to mugs is just an extension of that. They want to know as much about all of their guests as possible (whether or not this is good is debatable..and I don't really want to deabte it
), including how much soda each consumes. This allows them to personalize not just the guest experience, but their marketing as well.
I agree with Kevin when it comes to Disney not currently perceiving this as an issue. Maybe if they implement this technology, Disney will determine this is actually an issue...maybe they'll simply verify that the mugs are a cash cow, even if people are using them again and again. Bottom line is, they're studying it now, and will in the future.
In any case, Disney's ability to collect and analyze data about their guests is un-rivaled...no other company I have ever known has as much data on their customers as Disney does. Again, while their access to this much info is debatable as a good or bad thing, knowing so much about their guests is what allows them to fine tune some of the magical details we all love (as well as add extra money to the bank).