Welcome home Ellen
It's a flip of the coin- IF there is a new points conversion (it is in the works but who knows if and when it will be introduced), I strongly suspect you will be better off having bought beforehand (assuming you intend to buy resale). I know the waters are a bit murky about the whole thing, but assuming you buy at a good price I don't think you can get burnt and beforehand may be the only good time to buy resale.
Again, no one has a way of knowing anything for sure, but Marriott has no financial incentive to penalize any current owner (which is why I think they will treat all owners the same initially, which is what I have been told will happen by one source, for what that is- or isn't -worth) and, actually, has financial incentive to treat all current owners the same (insofar as they will have more people to get the program off the ground and collect fees and will avoid antagonizing any current owner, all of whom are prospective future buyers when they do begin expanding again). However, there is a financial incentive to penalize future resale owners, so now may be a limited window of opportunity. Of course, time will tell.