In the case of the Nacra 5.5's, the problem was that the sloop rig was different from the unirig, so you couldn't just switch back and forth from sloop rig to unirig by simply removing the jib.
The Formula 16 has supposedly overcome that problem.
The balance of the design makes it possible to simply remove the jib and be able to uni without have to readjust the world. The addition of the spin in either configuration is what now allows them to 1or 2 up without significant performance issues in total. Without the spin, the small loss of sail area by taking off the jib is not proportioanl to the loss in crew weight. The added performane you get by having 4 hands to properly trim everything helps make up for the weight pennalty of 2 crew.
For me sailing solo is fun, but I got into this for the social aspect. I would much rather go out with someone else on the boat when I race or even just fun sail. Whether it is just building on your crew work, or training somebody new who will hopefully get hooked and get into sailing as well.
Just my view of the subject, but it is a concern as there seems to a building argument/division in our budding class about solo versus 2up that is going to cause problems.
