A super light and strong kite line, so when the wind is nada on the beach, you can rig up 1,000m lines and fly off high air currents. Fancy kite resorts will have a stable of rental kites moored to a floating platform high in the air. You just bring a board and harness, hook up to a kite (they'd only need to be 3 square meters or so that high) and ride. Tangles? Um... I'm sure there would be a sci-fi solution for that, too.
Or just borrow one of these kites and REALLY go flying:
In stunt kites, Skyshark
makes a couple standard lines of carbon frames for kites made all over the world. This is nice because instead of carrying spare parts for each rod in all my kites, I can carry a few uncut Skyshark rods and then cut them to size when I need a replacement. So I wonder if the kiteboarding industry will standardize on some part, like the LEs, struts, or bladders to save money and make replacements easy. The kite frame company could make a standard line of leading edges and struts and kitemakers could use them as a starting point for kites.
Stunt kites also have a thriving "boutique" industry of lone kitemakers who build custom kites. They're not cheap, but it's cool to be able to design your own sail
, consult with the maker on the exact kite you want, and get a much higher quality kite than something made in a factory. I love my twin JoE Talons
-- they perform on a whole different level (wind range, trickability, agility, durability) than larger-market kites. I'm sure you can get custom kiteboarding kites now, but it's not the norm.