As we've been talking here, I can foresee a few potential minefields for Marriott owners in some of the popular MVC locations where VSE has no presence - places like Aruba, Hilton Head, Newport Coast, etc.
For example, Aruba is already difficult to book in prime winter season in the DC because those locations are ineligible for the DC Trust, so the only inventory that shows up in the DC Exchange is inventory that Aruba owners have elected for points. There is no Trust inventory. Since VSE has no presence in Aruba, that will likely be one place a lot of VSN owners want to visit, increasing demand/competition for the already limited Aruba inventory. I don't think somewhere like Maui Ocean Club will be impacted much, since VSN has three resorts of their own there, so VSN owners wanting to go to Maui have less reason to choose to elect for DC points, whereas those wanting to go somewhere VSE is not will want to elect for DC points, putting more strain on those locations. I think the majority of the DC demand from VSN owners will gravitate to the popular locations where VSN is not.
The same thing could happen in reverse at the locations VSE has where Marriott is not - namely Mexico, St John, and Harborside - but if that inventory which is open to DC users is dependent upon VSN owners electing for DC points, it may take longer for the inventory crunch to happen at those locations.