According to wii.qj.net, there maybe more primes in the metroi games.
Nintendo's Kensuke Tanabe has intimated that Metroid Prime 3: Corruption may not be the last we'll see of the Prime series. Another handheld iteration may even be in the cards.
Speaking to Official Nintendo Magazine, Tanabe said,
We are always planning to make new games in the Metroid Prime series. Depending on the timing and the situation, we cannot deny the possibility of realising it on DS or DSi.
The last -- and only -- handheld entry in the series was 2006's Metroid Prime Hunters. Wii owners, on the other hand, saw the release of the Trilogy collection this year.