I think you can get a pretty light boat if you have money enough, the boat can also be stiff enough. We have in our workshop an A-cat ready to sail of 53 kg and we sailed it in conditions upto 20 knts and there was no problem at all to control the boat or even a problem with strength and platform stiffness. The boat was build in 1994 so it was already possible some 12 years ago.
The point is only the money you are spending on the project this boat was not cheap to build and cost us a lot of workmanship to achieve this.

Regards,
Hans