ScreenGems and Lakeshore are developing a fourth Underworld movie, so the feud between Lycans and Vampires will explode again. Underworld 4 will be shot in 3D and it's most likely a sequel, Producer Tom Rosenberg was already talking about it two years ago:
"When we did the 1st 'Underworld,' we imagined three - the 1st one, a sequel and then a prequel. The 3rd is a prequel, so the 4th would carry on where Kate and Scott Speedman left off after 2."
Producer Tom Rosenberg (in January 2008)
Rosenberg's quote is a bit dated, but more recently, Scriptwriter John Hlavin, who has been hired to write the script of Underworld 4, kind of confirmed that Underowrld 4 would be a sequel:
"I can tell you it’s not a prequel. It will satisfy old fans and excite new audiences, meaning that we don’t want to redo the first three movies, so steps are being taken to honor what fans have loved but at the same time introduce fresh elements."
Scriptwriter John Hlavin (in November 2009)
I hope Underworld 4 to be a direct sequel to Underworld 2: we'd see with Selene (Kate Beckinsale), who's more powerful than ever, and Michael Corvin (Scott Speedman), who's now a mighty hybrid, trying to clean up the chaos created by the death of the Elders.
Unfortunately this is still speculation, nothing official yet, but plot details of Underworld 4 should surface online quite soon! We will then have a better idea of what to expect in the movie Underworld 4.
:)