phltraveler

Yes. Starting August 1st, according to the new info in this thread your combined MR + SPG night totals will count towards the 750 night + 10 years as plat requirement to get old Marriott Platinum/new Marriott Lifetime Platinum Premier. The meeting nights would not count until August 1st as well, however any nights earned in MR (whether via stays or meetings) would be eligible in the combined total for 750 effective August 1st.
OP has three possibilities. One of which is 750 night relevant.

1) OP chooses to earn lifetime SPG platinum under the old rules (10 years at Plat + 500 nights). This would require him to mattress run 56 nights before the end of 2018 to hit 500 nights total. This would get him lifetime status at the level that current elites qualify for at 50 nights/year.
2) OP chooses to earn lifetime Platinum in the combined program after the merger. This would not require him to get all the nights this year, but it would require him to get 600 nights total (combined legacy Marriott + SPG). This would get him lifetime status at the level that current elites get at 50 nights/year.
3) OP goes for a huge stretch goal and tries to earn old Marriott Lifetime Platinum, which is Premier Platinum (75 nights) before the end of the year. This was originally impossible for SPG elites, but Marriott relented and now SPG elites have ONE shot in 2018 to earn lifetime Premier Platinum. This would require OP to earn 750 nights + 2 million points in Marriott alone before end of 2018, or to earn 750 nights + 10 years of Plat in combined activity between the Marriott and SPG programs before the end of 2018. This will get OP lifetime status at the level that current elites earn in 75 nights/year, a grandfathered status that won't be possible to achieve in 2019 and beyond.

Option #3 is a huge stretch for OP on his Starwood nights alone, because at 444 SPG nights, he would require 306 more elite nights in 2018. This would be physically impossible to earn butt-in-bed as Marriott will only credit one elite night per room (no credit for up to three rooms like SPG) and there aren't 306 nights left in 2018.

However, OP would get credit for any Marriott legacy activity he had (could be 0 nights, could be 200) AND under the rewarding events structure, OP gets 10 nights credit for every meeting booked at eligible properties. People on the MR board on FT have booked $60 meetings for one hour, many were able to no-show them (pay for the meeting, not show up to the meeting, and still get the 10 elite night credit), and essentially "buy" the nights at $6-$10 per elite night, which is way cheaper and easier than earning them via stays. Even if you had to show to the meetings, nothing would stop you from having a legitimate meeting once a week, or having one hour meetings where you merely hopped on the wifi and did some work or browsed the web casually. See later posts in the thread [Marriott] Platinum Status in Eight Days and $800 - No Stays Required

Assuming OP averaged $90 a meeting and wanted to "buy" his way to Lifetime Platinum Premier this year, it would require anywhere from no meetings (if he had 306 nights, but OP calls his legacy Marriott activity "not so many stays") and $0 to 31 meetings (OP has no MR legacy activity, 31 meetings * 10 elite nights per meeting = 310 MR elite nights + 444 legacy SPG elite nights = 754 nights combined effective August 1st + his existing 10 years = Grandfathered LT Premier Platinum in new MR - at $90/meeting, this would cost $2,790).

Personally I would not spend the latter amount, but I might spend up to $1500 to lock in a discontinued higher elite tier. MR has made minimal difference between Plat and Plat Premier in the combined August 1st program at this point, but others have pointed out how as airlines consolidated and time passed, airlines created more of a difference between their elite tiers, leading some to regret that they didn't chase a higher lifetime status earlier (when they were traveling more or while it was still possible). Marriott may choose to make a greater difference between LTP and LTPP in the future, and I strongly believe they will.

The rub is that Marriott may change their rules on Rewarding Events come August 1st. Existing night totals (including Rewarding Events nights given @ 1 meeting = 10 elite nights) will count towards the lifetime qualification totals and MR + SPG combined night totals will count for this, but meetings after August 1st may no longer universally earn 10 elite night credit (no crystal ball, but rumor mill is MR will only give 10 elite night credit for the account's first meeting in a year, and then only 1 elite night per meeting thereafter).