In addition to the technical sorting out of the boat for the US region...

The Fox suffered a class problem as well. About that time... Hobie Alter set forth a widely published opinion about what the Hobie Class racing program should be in the furure. He sort of foretold the future. He argued that the racing class should focus on the Hobie 16 with no spinaker and the Hobie Tiger. The 20's, 18's, 17's in their racing classes would eventually migrate to one of the two featured Hobie classes. The Fox and FX1 were not really considered as part of the program for the future. With out the appeal of a strong class forming behind the Fox.... the boats were resold back to the EU.

Finally, the fate of any 20 foot spin class must deal with the smaller number of teams that want to sail the boat.
Figure about MAX 10 Tornado Teams in the USA and Canada.
20 Nacra teams that compete at Nationals.
20 more nacra Teams that race but don't travel much ... = 50 teams! It is not clear to me that another boat in a formula class would increase the numbers of sailors on 20 foot spin boats. The competition from the F18 class for interest is pretty intense.

The 20's remain popular for distance racers... and regions with light winds... (Chesapeake Bay for example) (nothing like a tall mast in light breeze). The F18's have NO foothold on the bay as a racing class.