UPDATE: 31/3/07The magazine has been released and it seems the game is indeed a Wii exclusive and will feature a 2 player / online mode.
There has been rumour ciriculating the internet that a sequel to Sega's NiGHTS will be released on Nintendo's Wii console. The rumours pointed towards the exclusive to be reported by gaming magazines. And now a preview of the April edition of Sweedish gaming magazine "Gamereactor" reveals the following:

Whilst this is probably not yet 100% confirmation, it seems likely. Look out for more information shortly.
Source: GoNintendo