It probably goes without saying, but a franchise doesn't manage to spawn 8 separate TV shows and 12 major motion pictures without a whole host of ideas getting batted down in the process. For every hour of Star Trek you've managed to watch, another 5 or 10 probably ended up in the various bins that ideas must leap past on their way to getting made.
It probably also goes without saying, but a franchise that's built its entire premise on the limitless wonders of space exploration will have no shortage of new ways to realise the galaxy of possibilities therein. Across time, space, science and the human condition, virtually nothing's ever been off the table for Star Trek, and writers from within the franchise and without have pitched the next great sci-fi venture over the years.
While we can look at everything we have had and be delighted, looking at the various shows and movies that never quite made it is equally as fascinating. Outlandish adventures, in-depth character pieces, even ideas that would have pushed the canon into radically new territory and timeframes.