Guide is probably referring to the fact that Dec will get 2018 points now that they can bank, and 2019 points Dec 1. SO for all practical purposes having more points for use Dec 1, 2019 to Nov 30, 2020. Which can be of benefit to someone purchasing right now, August will be in it's 2019 use year. If you are already an owner, though, I definitely stay with one use year and not manage 2
DVC accounts. My life is complicated enough.
I personally wouldn't care for a December use year, not that there is anything specifically wrong with them, but it would be weird to me to have your use year almost a year off from calendar year. But functionally, it is the same as any other use year, no specific advantages or disadvantage to any other use year.
If you really like the Riviera rooms and location, go for it, even with the resale restrictions. I love having my 11 month advantage at OKW, even though that may not be as popular as other resorts, because I love staying at OKW. I still think the best strategy is to buy at the home resort you'll want to stay at most often for that 11 month booking window. And it will be especially important for studio people, since studios do tend to book up first at every resort. The restrictions will only really affect you if you sell, and so far, I don't think we know what overall effect that will be.