i don't think they'll made a "death lens" for the hmc, their idea is to have a professional look with the HD cameras, hence the reason there's the 16x9 lens then the Century X-treme fisheye, because the consumer is looking for a more professional look, the more barrel distortion and widenss you give the lens, the more vignetting it will have and just look gross in high definition.
Most likely I will go for the 0.45x century fisheye. Together with the natural wide angle of the HMC it will give you about 107° of horizontal viewing angle. I think that's enough.