I can see that aluminum would be a good material, but the joining of it could be a bit problematic. I have a lot of experience in the testing of metals, and know that a good water-tight, structual aluminum weld is often very difficult to make. I know that traditional wire-fed welds on material thin enough to give acceptable weights for catamarans are very, very tough, and the skill level required would be on the level of 1 welder vs 3 fiberglass mechanics. I give that as a ratio as welders working today with that skill level do not come cheap, and their numbers are declining.
I really think that to achieve a top quality product there will have to be the use of new technology such electon-beam welding for this. I've been around it and anything that can produce a flawless weld joining the foil of a cigeratte pack to a foil gum wrapper with no distortion....well, it's good. I know that the similar metalurgical techniques used in the manufacture of golf clubs today has potential elsewhere, just as a lot of it came over from the defense/areospace world in the 1980s.
Just my thoughts.

Rich