A full model of Sylux from Metroid Prime: Federation Force has been discovered by Wikitroid user Bearborg, who experimented with the in-game cameras to show a different angle to the secret cutscene from the very end of the game, where Sylux infiltrates a research station to steal a larval Metroid. This is the first time we have seen Sylux in full from the game, as the original cutscene is made to be shown from a first person perspective.
Sylux was first introduced in Metroid Prime Hunters, and was also confirmed to be inside the ship giving chase to Samus in the post-credit scene of Metroid Prime 3: Corruption. Sylux is also rumoured to be in the upcoming Metroid Prime 4, due to the events of Federation Force, as explained above.
UPDATE: We have updated this article to include a gallery with some additional shots of the model, courtesy of Bearborg.