Darker? Please no, thanks. I would not want to watch that. One of the reasons I (and I think many other fans) like Star Trek is that it always presented a more or less hopefull and positive view of the future. Trek already has some scenes / episodes / movies where it went dark enough. I donīt think making a whole "dark" series to a great extent would be wise. For what itīs worth...I always saw ENT as already beeing "darker".
The world is a far darker place now, my friend. Star Trek was born in the idealism of the 1960s. Now we live in a far darker age. BSG was the last successful true sci fi show on tv and it was dark. Maybe a dark and exciting new star trek show is needed nowdays.
Stargate Universe (SGU) was dark but it was boring and the writing could have been better and it did get better in the 2nd season.
So the next Star Trek series need to be darker, but better written than those of SGU and Caprica (i was bored to hell watching that show)