About a decade ago, around the time that the reimagined Battlestar Galactica was announced, I started thinking how TOS could be reimagined in a similar way. Not to "dark it up", but how to bring in serialized storytelling while staying true to the intent of the original.
One of the things that TOS featured heavily, especially in the beginning was an emphasis on the loneliness of command, so I started with that. I looked at one of my favorite movies on the subject, 12 O'clock High, for inspiration. The Enterprise wouldn't be the "flagship of the Federation" or even the best ship in the fleet. She was just a ship, and at the beginning of the series, she would be a broken, 20 year old ship. She had been a great ship under Captain Pike, but that was over a decade ago, and two poor COs after that, she had a demoralized crew, and hadn't even left space dock in a year in a half. Starfleet is even considering cutting their losses and decommissioning her.
That changes when a Starfleet probe discovers an ancient and technologically advanced ship drifting through space - towards Klingon territory. The limited information that the probe is able to get tells them that they can't let this ship fall into the Klingon's hands, and a ship needs to be sent to investigate it, salvage it if possible, and destroy it if need be. The Enterprise, true to form, is the only ship close enough with the speed to pull this mission off.
Commander Kirk, who is a hot-headed, but brilliant and driven XO is promoted and pressed into service as the CO of the Enterprise and given this seemingly impossible task.
He's given a vulcan XO, Spock, who is familiar with the ship, having served under Pike years earlier. This is, in Kirk's eyes, a temporary placement, because the man who he wants as his XO, Gary Mitchell, is the ship's Operations Officer, but Starfleet overrides him due to Mitchell's reckless behavior. (In his first scene with Kirk, he's brought back to the ship in handcuffs - deliberately referencing a similar scene in 12 O'clock High).
Anyway, long story short, the Enterprise intercepts the ancient ship, discover that it is the 30,000 year old First Federation starship Fesarius. The Klingons intercept them, and the ship winds up falling into Klingon hands, but not before the Enterprise crew is able to download star map data which seems to show potential caches of First Federation technology - and it would take about five years to travel to these planets. A race is on, since the Klingons would have this information as well.
The idea is that we would get to see the Enterprise turn into the ship that we know and love, but it wouldn't start out that way. It would be Star Trek deconstructed. All the pieces would be there, but wouldn't (at first) fit together in expected ways. The "Big Three" at the beginning wouldn't be Kirk, Spock and McCoy, but Kirk, Mitchell, and his female Command Master Chief, who was a mentor when he was an ensign. Spock and McCoy would be there, but they wouldn't be friends with Kirk, and Kirk would see their advice as more antagonistic than helpful.
The one major change would have been with the Klingons. The original Klingons had them as the Soviet Union to the Federation's United States which isn't as timely as it used to be. In my reimagining, the Klingons would be more of a mirror of the Federation - an empire built up of many races; some conquored, some there willingly, and even some human worlds. They would be bound by a common religion, the followers of Kahless, and there would be elements of fanaticism among them, although not all. The main difference between the Klingons and the Federation would be that the Klingons don't have the prime directive, and they willingly share their technology, as long as you are part of the empire, making them appealing. I wanted to make the Klingons less clear cut bad guys, and allows for variations among them, instead of a monolithic warrior culture.
Anyway, there are lots of things wrong with my ideas, but it's the kind of TOS reboot that I would want to see - taking concepts from the original to build a framework on to tell new stories.