... as long as they conform to the still current "box rule" they are legal, rule 8 (hydrofoils are not permitted) cannot be enforced properly since a hydrofoil cannot be conclusively defined other than "the spirit of the rule".
Or there is another way to lok at it. Rule 8 was created when the first pictures were sighted of an A Cat flying on traditional/classic hydrofoils in the form of v-struts and t-bars. So when the experiments with canted and curved boards started, so did the discussions as to what was and was was not legal. Rule 8 needed clarification in order to prevent an a cat from flying and the box rule was born. It can then be argued that whatever conforms to the box rule is not a hydrofoil, since that was the purpose of the box rule.
But thats just my opinion.