The decision by Marriott to eliminate rollover nights and elite buy back will have an effect on who earns elite status with Marriott Rewards. It will be harder for moderate travelers to reach the top levels of the loyalty program. Whether it was Marriott's attempt the 'thin the herd' as some Insiders have suggested is little more than speculation. Marriott has been rather circumspect when explaining their reasoning, saying only they want to make sure those with elite status "enjoy their Elite benefits such as lounge access and room upgrades on a consistent basis."
Getting rid of elite buy back will mean folks who no longer earn enough elite nights credits each year will drop a level when the status year resets. Losing rollover nights will have a similar effect, in that only nights earned in the current year will count toward earning or retaining status.
It is important to note that before 2016, redeemed nights did not count toward earning or retaining elite status. So while the loss of elite buy back and rollover nights will hurt, the ability to count nights spent on points helps a little.
For those of us in the USA, the Marriott Rewards credit card goes a long way toward earning elite status. Just by having the card, a member is guaranteed Silver Elite status through the 15 elite nights the card grants each year. Getting to Gold for cardholders only takes 35 nights, and some of those could come from the additional 1 night earned per $3000 charged to the card. Depending on how much someone uses their MR credit card, it would not be unreasonable for someone to earn 20-25 nights from it (counting the 15 from just having the card). Undoubtedly, some will earn more than this. Even with the loss of rollover nights, this means one could achieve Gold Elite status after staying 25-30 nights, some of which could be redemption nights. While this will be difficult for some, I suspect a large number of Insiders who have yet to reach lifetime status may find getting to Gold is within reach. Since the majority of benefits, specifically lounge access and room upgrades, kick in at the Gold level, I don't expect there to be a significant drop in those numbers. I'm sure there will be a drop, it's just hard to know how big.
Reaching Platinum might be a different story. Even with the credit card, it will still mean staying around 50 nights (depending on credit card spending). While road warriors will have little trouble reaching this in a few months, leisure travelers could be hard pressed to attain this level from year to year.
While I'm sorry to see rollover nights go, I'm not convinced it will lead to a drastic 'thinning of the herd' of Gold elites. The CLs will be just as crowded and the competition for upgrades just as fierce. It might mean better odds for upgrades for those who manage to reach Platinum status, if as I noted above it becomes more difficult (on a relative basis) to achieve.
As with most things, we'll find out soon enough.