You can link the accounts and transfer points between accounts currently. Each Starpoint converts to 3 Marriott Rewards points:
Link Marriott and Starwood Accounts | Marriott Rewards
As verysuiteboy shows you, you can “link” your accounts. However, the word you used was “merge” which I take to mean “combine” into one. That is still not possible. Lifetime points and nights remain associated with the program in which you earned them. The programs are still operating separately, although you can move points back and forth at 3:1 or 1:3 ratios. I thought this might be worth clarifying, as those who are pursuing lifetime status have opted to stay in their lanes because nights in the other lane don’t help you.
Whatever you decide, good luck and happy travels!
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