Even in the old system with a KTTW card, park ticket (and using FP-), plus using any CC for any purchases while at WDW, WDW could already easily track most park visitors. MB may make it more efficient but does not add much to this data gathering and is no different that CC, store reward cards or programs, and other such systems currently in place all over the US.
Sort of, kind of.
It's a lot harder to aggregate data from disparate sources. So, if you were using your KTTW card as your ticket, your room key, and charging everything to your room....then, yes...they could do some similar things. But not everyone (and maybe not even most people) were doing that.
For instance:
My family of 5 typically buys their tickets from UCT. We are DVC members, who stay on property, and we typically do not "room charge" everything. We either use specific credit cards or gift cards to pay at POS. We make a ton of ADRs. We have often used photopass. So to get any "tracking" for my family, you'd have to hit your resort system, your POS system (maybe, if we used a CC), your ADR system, your photopass system and you'd NEVER be able to track our tickets, because they never would have had a name linked to them in any Disney system. That's a lot of trying to link up disparate systems..and not all that easy.
Ignoring the active sensor abilities of the MB (meaning, they can LITERALLY track your position via RFID signal, if they so choose), MB's are going to "encourage" (as in, pretty much mandate) a single source tracking ability for most things. Because now, with the advent of FP+ (the carrot), you pretty much have to link your tickets to your MB's if you want access to it...and link all THAT within your DME profile. And the MB is your room key. And your FP- mechanism (assuming FP- stays around for a bit). And it acts as your link to "Memory Maker" (aka Photopass +). And your linked DME profile acts as your ADR tracker. so is an easy trace back. That's a LOT of data in, potentially, one place.
Charging still is optional...for now. We'll see if they start providing some sort of carrot to encourage charging back to your room....
Keep in mind, I'm not commenting on the "good/bad" of it all. As a professional IT person who does a lot of analytics, I think it's a neat concept. I'll have to see it in practice (8 DAYS!) to see if I like the function. I have no strong opinion on it's ethics.