So I'm a little late to the game on this info... Did not realize this distinction between SPG and MR LTP transferring inequitably into the new combined program. I assumed LTP = LPT, which was bad enough, but now realizing MR LTP = LTPP while ANY SPG LTP = LTP I have to say it is difficult to stay calm. As an SPG LTP with 836 nights and 12yrs Plat, and wanting to give Marriott the benefit of doubt, I can only hope this inequity is simply a GIANT FREAKIN OVERSIGHT.
Note that during the same 12yr period I maintained Hyatt Diamond status in addition to SPG Plat, yet had only 2 Marriott stays, i.e. I have a great deal of control over hotel choices even on biz travel. With LTP-Minus (I agree with MSPeconomist) under the new program locked in, and no apparent path to LTPP, I can shutdown Marriott stays as I have in the past with no impact on LPT-Minus status. I am free to focus my stays elsewhere with no downside related to the new Marriott program.