I actually wouldn't mind a new line of Alien story, at least not as much as the alternatives. I don't know about a 'reboot' though, where the original tetralogy is forgotten for the new story. I'm intrigued by the notion of an "Alien 5" that is the start of a new story and plot line though (rather than being more of a continuation from A:R and of Ripley's journey).
It would most likely have to be limited to post-A:R, given the dialogue in that movie indicating that apart from Ripley's encounters, there have been no trace of the species.
A new line, though, could breath new life into the series though, should it be given the proper care, budget and attention it deserves (something, that may be to much to ask given how the series was treated with the AvP line).
A new plot line would free the story from being defendant on Ripley. Don't get me wrong, I don't dislike Ripley, but she is, at this point, a burden on the series. Hell, she died once, and now her clone is finally back on Earth, bringing her story to a close (as Earth had been her destination from the very start).
So, no, I'm not for a reboot in the way that you describe it. I think something to the effect of what I described above would be interesting and rather exciting (again, should it have the proper treatment, of course). Something like that has a great deal of potential.
