They don't really care about inventory in the DC at this point. Do they make more money if there are more Maui units traded in? Maybe some from "skim" but it's peanuts compared to a $30K points sale where they buy points for $2-$3 at ROFR and sell for $12-$15. Then they also get your inventory.
The DC exchange has been up and running for 12 years and has a high volume of exchanges already. They are playing the long game - they are now getting tens of thousands of new owners who they can try to sell a new shiny object... "You want access to 60+ high-end resorts? Just buy X thousand points and you're in! We love Vistana weeks, and your week will get you 20+ days elsewhere"
Their system seems to work well. Just look at what VAC stock has done since the spinoff in late 2011... I own multiple Marriott weeks, but haven't purchased any from them. I haven't purchased any points from them. I don't think the economics are in my favor with their pricing (Vistana pricing was a bargain compared to MVC, IMO). But plenty of others are buying from them for their own reasons, so I just buy the stock and plan to hold it long term
(this is not meant to be financial advice or an endorsement to purchase risky securities in any way*).
I'd be very interested to hear their earnings call Q&A on May 5!
* The value of shares and investments and the income derived from them can go down as well as up; Investors in stocks may not get back the amount they invested - losing money is a real risk; Past performance is not a guide to future performance.