Several years ago I went on the National Geographic Endeavour
from Easter Island to the Cooks. The ship had a fully equipped dive setup, 110 passengers...and only five divers. It was like having your personal cruise-dive ship and provided a chance to dive places nobody gets to (Henderson, Palmerston islands, etc.)
The NG/Lindblad company has a new ship, the Explorer
. As part of its itineary, next March-April it will be doing a trip from Dar-es-Salaam to the Seychelles. This offers a chance to dive Ibo island (Mozambique), Mayotte, northern Madagascar, and the outer islands of the Seychelles, including two days at Aldabra. This is high-class "adventure" cruising, with the only drawback being the cost. But for those who want to save up, it's another chance to go some places nobody goes. See www.expeditions.com
and go to the Indian Ocean itineary page.