There really isn't much left to improve. Perhaps some computer and carbon fiber means to better harness and control flex and twist factors. We can already make boards so light that they become too light. Perhaps some sort of light, strong and consistent blank material or molding process so boards can be super repeatable and become more dialed in. Robotic shaping machines again to get the boards super consistent and make super fine adjustments on custom boards possible without the human touch.
More than anything today, we need better surfers. The boards are great but the average surfer SUCKS more than ever. The average surfer today doesn't even try high performance equipment. I would have been fucking embarrassed to ride a longboard, midlength or foamy in my teens 20s or 30s. Would have gotten laughed out of the water and shut out at the peak. Not today's surfers. Bunch of fukking donkeys clogging up the lineup using lots of extra foam to boost wave counts and mask their total lack of ability.