Check your assumptions, Pratima.
1) There's no committed date for when Marriott Rewards terms will change.
2) There's no promise that Marriott Rewards terms will change materially. (Remember, Marriott is the acquiring company, so the resulting combined program is more like to resemble the current MR than the current SPG.)
3) There's no promise that the qualification requirements for lifetime status will change even if other parts of the MR program are changed materially.
4) Finally, if you don't stay at Marriott hotels often enough anymore to see an obvious path toward earning 20k points from stays, how important is it for you to raise your LT status from gold to platinum, really?