AC is the pinnacle of sailboat racing. The wing is the pinnacle of tech for sailing. All the design work has involved a wing and a complete structural redesign would be needed for soft sails because things like sheet loads change dramatically.
The old wings were 13 stories high, and they are saying the new smaller wing will allow a smaller crew to step the wing. They seem to be implying that the new wing won't be as proportionally tall, making the boat not so overpowered. They were starting to de-power in winds above 12knts on the 72s. Would be nice if they could stay out sailing in solid 25knts. wind speed. The wings are still efficient in the stronger winds and the manageable sheet loads mean sheeting in and out can be done quickly. Cranking a giant soft main back in after easing in a gust while trying to foil upwind would be a huge problem to solve.
Also, there seem to be 6 potential teams going for those 4 spots if you add in the French and English to the list.. There is either going to be a lag time after the 45 racing when the top 4 build their boats, or some one may build a 62, but fail to qualify.