The OP makes some good points, but so do others.

The fact is that anyone who doesn’t have 10 years or close of Platinum status in either program or combined has little leg on which to stand. I am most fortunate that the combined calculation allows me to reach Lifetime Platinum Premier/Titanium status.

That being said, the fact that Marriott is only making LPP/Titanium status achievable for this onetime sweep in Jan 2019 is quite unfortunate and perhaps ill-conceived; after all, were people able to still achieve that status in coming years, there would be little complaining.

Personally, I think Marriott made this mess for itself by foolishly creating the Lifetime Plat Premier level in the first place. The fact is that pre-merger Marriott Platinums (requiring 75 nights) didn’t have half the elite benefits and perks that even the new post-merger Platinum status has (requiring 50 nights). Had everyone just been swept into a Lifetime Platinum tier with these much enhanced Platinum benefits, with everyone continuing to still be able to earn that Lifetime Platinum status, Marriott would have saved itself a lot of hassle.

That is now neither here nor there. But it does argue for Marriott to perhaps reconsider ending its Lifetime Platinum Premier/Titanium qualification period. That would end the discussion, even if Marriott compromises and significantly raises the qualification for future consideration.