There were some chatter last year that Nikon may bring back to life their underwater Nikonos product line. Tetsuro Goto (Director of Laboratory R&D at Nikon Japan) had this to say in an interview with Focus-Numerique: “personally I think the Nikonos reborn in the future”.
Trademarkia lists the Nikonos trademark as expired as of 08/22/2008 which probably means that Nikon has no plans of a new digital underwater product line:
The Nikonos trademark was registered back in 1967.
According to about.com, trademarks must be renewed every ten years:
"The term of a federal trademark registration is ten years, with ten-year renewal terms. However, between the fifth and sixth year after the date of initial trademark registration, you must file an "affidavit of use" and pay an additional fee to keep the registration alive. You must also file an affidavit and pay a fee within a year before the end of every ten-year period."