OK, at the risk of putting my foot in my mouth... I also hope that these changes are more theoretical than actual in terms of people taking advantage of them.
Years ago... decades, actually, when I purchased my first SVO (now Vistana) timeshare, one of the reasons I decided to buy it, instead of buying in the Marriott program or any other program, was that I felt that both the Westin resorts themselves and the guests who used them were of a somewhat different sort than those at Marriott properties. The Westin weeks were pricier than the Marriott weeks, and it just seemed like the guests were of a higher caliber, with fewer kids running around screaming, etc. That sounds a bit elitist and maybe it is, but I have found the environment at the Westin properties to be less chaotic than at the Marriott properties, and that's something I value.
Nearly twenty years later, I still believe this to be true, on the whole. I have family members who own in the MVC system and I've spent lots of time at those resorts too, and I just feel like they attract a different crowd. Not saying one is better or worse, just that I usually prefer the Westin guests and vibe to the Marriott guests and vibe, to the extent there is a difference.
So I'm not looking forward to any great invasion of folks from the Marriott side and hope it doesn't really happen.
This isn't intended as a slam on anyone, and of course it's a generalization that doesn't apply universally. But I worry about the homogenization of the network, which I think will be to the detriment of those of us on the Vistana side. (I am certain there are Marriott owners who think THEIR resorts are better... different strokes for different folks!)