Make a sci-fi series for folks who prefer fantasy over sci-fi? That makes no sense at all.
Well, you want to target as broad a group as possible. If the focus is strictly on hard science fiction fans, then you are gutting off potential viewing audience, and you are setting yourself up for failure.
The idea of targeting just one demographic is not really going to work in this day and age because people have too many options now. I mean, as Warped9 mentioned Star Wars is really space fantasy, that works for a number of demographics, especially children.
Star Trek's fanbase can be very fragmented, so appealing to a much larger audience will be critical to the success of any new show.
Logic failure, as was stated before one of the reasons making trek harder is for appealing to a wider audience.
One of the reasons people love HBO "dark and gritty" shows is that they make sense.
People behavel like people and things tend to have actual consquences.
You're talking two different issues. One is scientific factors and the other is audience appeal. Audiences, generally speaking, do not care if something is scientifically accurate, so long as the world is consistent and the characters believable.
For me, "hard sci-fi" refers to more realistic science, not consistent application. I know the term gets tossed around, but I generally work from a fairly strict definition. I'm sure I missed the current working definition for everyone, but there are different classes to that term.
Also, "dark and gritty" should be not be a requisite to create consequences or believable behavior.