phltraveler

750 nights will be required to hit the legacy MR Plat status, which will only be achievable by end of year 2019 2018. If you do such, then it will map to grandfathered Lifetime Platinum Premier status in the merged program, which will not be possible to gain in 2019 onwards.

However, at 444 nights, this would require you to rack up 306 nights before the end of 2018. This assumes you have ZERO legacy Marriott activity. See the thread SPG Lifetime Platinums Can Now Qualify For Lifetime Platinum Premier Status.. Your qualification criteria would be 750 MR + SPG nights and 10 years as plat before end of 2018.

Now, if you have some substantial stay activity at Marriott - say you had at least 200 nights - then you'd be only 106 nights away from earning old MR Plat/new Plat Premier status. 106 nights would be a lot on a mattress run alone, but as of this time, sub-$100 meetings at eligible Marriott properties earn 10 elite qualifying nights. This would mean you could use a combination of cheap meetings and mattress run to hit the goal. Whether or not this endeavor is worthwhile I leave to you, and it's possible that MR may change Rewarding Events come August 1st (SPG/MR program merger) to not provide the 10 elite nights any longer.

However, in the merged program, Lifetime Plat and Lifetime Plat Premier are minimally different. Lifetime status does not confer the Suite Night Awards (you have to hit the 50/75 night thresholds in a year to get SNAs), and the only differences between Plat and Plat Premier (at this time) in the merged program are a 75% points bonus vs 50% points bonus and Plat Premier having the 48-hour guarantee (to get a room at a ridiculous rack rate at a sold out hotel). Lifetime Plat in the new program will still be possible at 600 elite nights + 10 years as plat...