PowerGenix has released a rechargeable batteries using NiZn (Nickel-Zinc) cells. The cells are rated to be 1.6V (vs the 1.2-1.3V of NiMh batteries) and are said to do very well in high current draw situations. Although they might not last as long as some of the best NiMh batteries out there (Eneloops), strobe charging times should go down due to the higher power output.
Someone will have to test this to see if it provides a practical gain vs Eneloop NiMh AAs for underwater photographers. A charger and 4 AAs retails at $49.99 but is available on Amazon for around $24.