They have built in their fees. Everytime you deposit a week into points they skim points off the top which is a fee (or profit whichever you prefer). When you exchange for a lockoff, the sum of the two lockoffs is a much higher point total than the points required to rent the whole 2 bed room week, so they are charging more points for that, so yes there is a lockoff fee. If you use points for daily stays, the sum of the daily points are much higher than the points required for a weeks stay, so they are charging fees for daily stays too. By not specifically charging x$ per lock off or daily stay it can be sold as free to members, but if you compare what your points outlay is for lock-offs and nightly stays versus a week in the same unit, you are paying a hefty fee in additonal points charged by Marriott to get "flexibility".
Marriott is charging you to convert,they will probably start raising annual MF's, they are charging you an annual membership fee, and they skim points every time you deposit and exchange. Marriott is not doing any of the wonderful flexibility options they tout for free, they are charging you each and every time you want to be flexible and use your points to exchange!
Imagining Newport for 3 prime season days, followed by 3 days at this hawaai resort followed by 4 days at another will IMO be just that, imagining. Every person they sell the points to will be assured that getting those things will be easy, but most if not all prime inventory will be reserved for a whole week before those wanting shorter stays ever get a chance at less than 7 day inventory. In the beginning there will probably be access to less than 7 day stays at prime resorts during prime seasons, but after they sell and convert a ton of people to points the competition will be so intense that getting any prime days/weeks will be hard. In fact I bet that it will be much harder to get prime weeks/locations than before points because Marriott will be able to sell those shoulder weeks as points allowing more people to compete for the prime limited inventory, because points is points no matter where they come from.