It just outlined how Trump tries to make his negotiating opponent look good when he grants a major concession to Trump. Trump does this by starting out demanding the world, and then accepting less. Recall all the TACO posts earlier, when people did not understand this tenet of negotiation.
I could see, just for example, a 99 year lease with a referendum by the people at the end of the lease term. Denmark will have saved NATO (and looked good to its fellow members) and have received a large payment (and looked good to its people) and not have surrendered ownership.