If I had to take an educated guess, I would assume that the hot water prep idea would be more noble than using ethanol, but this guess with little evidence to back it up. If I had to dream up an ideal high extraction prep method, I would imagine a water soluble long chain polymer with numerous lactone moieties pendant with the proper partitioning for kavalactones. As the room temperature root was mixed in water with those polymers overnight in an oxygen and light free environment during sonication, the kavalactones would gradually be siphoned off from the root and preferentially partition into the polymers at near the relative proportions a the traditional prep, yet at extraction efficiencies over 50%. Then I would separate out the plymers from the root/starch/ water mixture. Lastly, I would isolate the kavalactones by some means like 34 F precipitation or CO2 extraction. Can that actually be done? Who knows?
Do you think tequila worms would be a good partitioning agent for kavalactones? just kidding, I think