There is a rule that limits how close together the daggerboard tips can be to each other when fully down...foiling is not technically prohibited - they just made it much harder to do from a technical standpoint.

8.1 No part of each hull or hull appendages below the waterline shall be less than 0.75 meters from the centre line.
8.2 Movable and retractable hull appendages shall be inserted from the top or be capable of being fully retractable into the hull.

I'm not sure how 8.2 applies to rudders...I saw one boat with some small horizontal stabilizers on the rudders at worlds this year...so presumably this applies to daggerboards only?