The thing I am concerned about the most is giving up control - just go over to the Starwood board and read how Starwood has now taken away the right of owners to deposit reserved weeks in II - everything is now a 'generic' deposit.
They have also downgraded many ownerships with II all for the purpose of keeping owners within the Starwood StarOption (point) system.
There is no guarantee that any preference with II, or any other exchange, would be maintained. It could be but if Marriott felt that it helps their potential sales of whatever new, assumedly internal (read $$ for them) to remove that perk they can and will do so. There is nothing in any documents guaranteeing an exchange preference so it is an at will type bonus.
I hate speculation and I'm of a similar opinion as dioxide45 and billymach4. I'll believe it when I see it, and I think it would be a terrible idea since so many owners love the current system. Just compare the satisfaction surveys of Marriott versus Starwood...
Since it's been brought up, here is an example of how the Starwood policy would work in the Marriott world. I'll use NCV as an example, but you will get the idea... :
Owners depositing in II don't choose the week to deposit. In fact, even if you had a good reservation you need to cancel it prior to depositing. You would deposit a generic Platinum week and get a trading power equal to the average trading power of the season. For Platinum owners that means weeks 23-52. For Gold owners it would be the average of weeks 1-22. This may help some and hurt others. This may or may not include Platinum Plus weeks 26 and 52 but those owners are a small minority by definition. Marriott would retain control of what actually goes into II - obviously the intent would be to keep the "good" weeks for internal exchanges (that's why under this policy they would want weeks 26 and 52, although it's officially a different "season") so summer weeks will hardly make it to II and owners from other resorts using II will not get NCV summer weeks no matter how strong their deposit. All this of course, promotes usage of an internal system and allegedly props up retail sales.
However, any attempt to discriminate against resale buyers will hurt resale values. Most owners will realize this and will be quite vocal about it - which will hurt Marriott's retail sales. There are only so many units they can sell to buyers who are totally clueless about the resale market, especially when there is a right of recission involved. The "installed base" is too large to be ignored.
A completely different approach to promote retail sales would be to copy a different page from Starwood's book. For example, allow retail buyers to "retro" a resale unit (i.e., buy a retail unit and also get the ability to convert to hotel points on your resale unit). They can create an "Elite" program for multiple week owners with substantial perks (upgrades, waitlisting for reservations, no lockoff fee, no hotel point conversion fee, etc). Owners who will value these perks may view it beneficial to buy more weeks retail - and they already have a large customer base that likes the product. This is a better way that allows retail and resale markets to co-exist at different prices.
Ultimately they will do what they think is best for them - and they probably know better than us...