Boston’s Institute of Contemporary Art is in the final planning stages for its new home on the South Boston Waterfront, but everyone involved had to pause this week, when it was announced that the family which owns the land on which the new ICA will sit intended to sell the plot, after deciding not to develop it. ICA officials are saying that the sale should not affect their plans, since any new owner would be required to abide by the terms of ICA’s lease with the current ownership. Still, a new developer could choose to build whatever it wished on the non-ICA portion of the land, and observers are wincing at the possibility of a grand new museum surrounded by parking lots.