It's interesting to see how it shakes out. The members.marriott.com FAQ states uneqiovocally that Platinum Premier in MR will be matched to United MileagePlus Premier Silver. However, now that the
www.marriott.com refreshed page with new tiers has come up, the MR Plat elite level page (and PP level page) both state that MR Platinum and Platinum Premier (50 and 75 night tiers in the program respectively) will get MP Silver status.
I find that kind of odd, as it would be having the cross benefit to the UA Elites on MR side (UA Gold and higher now in post-08/18 program matches still to Gold, but that's a 25 night level now that no longer provides breakfast or lounge access) be less generous in the merged program while making the UA Benefit to the MR elites more generous (before, only the 75 night level in MR Level got it.)
The RewardsPlus page on the Marriott side is also down for updates until August 22nd, but
the FAQs still state that the match will be PP and higher to UA Silver. However if they are updating the main RewardsPlus page, it's conceivable that the information in this FAQ is outdated.
I guess we'll see in a couple days which part of the site is mistaken (Elite Benefits page for Plats, or members.marriott.com/RewardsPlus FAQ).
EDIT: RewardsPlus terms on MR side are pretty clear on this that they were updated for August 2018 (
link) and that:
Before PP was a criteria with published status and was invite only to top stay/spenders in MR, they did for a year or two match them to UA Gold. The 75 night level (Plat in old MR, Plat Premier in new MR) always got UA Silver under RewardsPlus.
Would I like Gold more as new LTPP? Yes.
Do I expect to get anything more than silver? No, and frankly, as long as Silver remains available to people with LTPP I'll be greatly appreciative anyways as MR/UA could chose to limit it to current year qualifiers like the 50/75 night awards like the SNAs.