While I realize you are trying to suggest a modest change with modest collateral impacts, I think that your suggestion will only stop the marathon walkers.
It will not stop those with enough points in a single UY to book their entire desired vacation, and who want to book in advance of their banking deadline. Those members will be able to "walk" a reservation by booking 2X the desired number of nights, holding that reservation until the cancellation period expires, then cancelling the unneeded days and banking the unused points.
For my early Dec vacation this year I booked more nights than I thought we wanted to give us flexibility when scheduling air travel. By some members standards, it was probably unethical to do so, but I held those extra nights until May when our airfare was booked, then cancelled. I am using those points for a vacation next May, so had no personal need to put them back into my account until June. We only have 175 points (but book a studio), so if we can hold extra nights for some period of time, I would guess many other members can as well.
And as to the marathon walking for months that some have joked they would try, those willing to engage in this practice would seem to be the smallest group of all. To walk, all you need is for that first night to be available. On another post, several members have posted finding availability as late as July for Saturday nights in December. Thus, even for NYE, there is porbably no need to start walking sooner than Dec.
Yes, you could start walking towards NYE now, but you could also get in line tonight for the Black Friday sale at
Best Buy. If you did so, you will be guaranteed first place in line, but sleeping in a parking lot for that many nights will probably not be necessary to achieve ths result. -- Suzanne