Two reactions.
I'm with Scarecrow here on setting an initial minimum weight and re-evaluating it at a later time.
Also I feel it is very important to reach an agreement on the class rules soon, even if some values may be subject to change at a later time. At least the general setup, structure and a pretty accurate "feel" for the values should be set. Currently we still have the change to do it the easy way. Once several 10's of boats, plans have been build c.q. sold the discussion will only get alot harder. For this reason I'm personally very willing to compromise on any values.
I strongly prefer to start relatively high and adjust it downwards later, this is alot easier to enforce at a later time as a heavier boat will always be compliant under any new rules. This is pure an organisational benefit.
With respect to rotomoulding. I think the technology is readily available at this time. I had a look over the state of things in the Kayak sector and the shaping c.q. detailing that can be had with rotomoulding these days is quite impressive. Currently in kayaks, builders make one design and produce the same product both in glass laminates and rotomoulded PE. There is no design difference in shape left.
For us it could be as easy as going to a rotomoulded kayak producer with any of the existing F12 designs and buy into their expertise and tooling. The hard part at this time is to find a party willing to invest in this and that requires economic viability.
Wouter