They already control everything that is deposited---Bonnet Creek is entirely UDI, and as of about two years ago or so, Wyndham no longer allows UDI owners to choose the week deposited on their behalf. Wyndham's RCI relationship is also a bit odd, because it is denominated in points. Wyn deposits things year round, and members request "generic points" exchanges year round, and Wyn/RCI "settle up" periodically. In other words, most members only have a generic points weeks in their RCI accounts rather than a "real week".
Wyndham is a bit of an odd duck in another way, because they release inventory into the Trust as soon as it is habitable, rather than reserve it for developer use until it is sold. To compensate, the Trust allows the developer to remove up to 90% of any remaining inventory at any particular resort at something like 90 days (though it could be 60---I forget). That provides owners significantly more flexibility about where they can book, but gives Wyndham the opportunity to pick off the most valuable things that aren't in high demand.
So, strictly speaking, at UDI resorts there isn't really "developer inventory". But, at this year's VOA annual meeting, Wyndham clarified their deposit policy. Wyn chooses units to deposit about 8 months in advance of occupancy, which is after Wyndham owners have had 2 months of "open season" booking. This tends to reserve the most in-demand weeks for owners, giving RCI the leftovers. However, Bonnet Creek is so big that, so far, supply has been outstripping demand much of the year. Holiday weeks have been obvious exceptions, but only the big ones. Even President's Week (now only 6 1/2 months out) has plenty of inventory remaining. Easter '09 only booked solid a few days ago, well into the free-for-all reservation period.