I did have a few ideas for a pg rated theatrical 'tlg' back when I thought that it would be post tlk2.
Basically, it involved a number of things that are now showing to be true in this show (simba worried about kion being a leader of the guard, simba not approving of non-lions in the guard, the hyenas starting to hunt and kill for sport.)
It would be about a group of returning hyenas, lead by the descendants of the original trio. They are not retreads of their old personalities. They believe that the pridelands are rightfully theres so they start killing as many animals as they can to intimidate simba.
In the middle to of the movie, they do a sneak attack while kion and his group is away. The prideland lions survive but just barely. Kovu and simba are barely able to walk and nala was almost killed. Also kovu and kiaras two cubs, who are introduced in the beggining of the film and seen a few times... I would plan on having them be some of the most loveable disney characters ever just to make what happens to them even more heartbreaking.... They're cubnapped by the hyenas and taken to the elephant graveyard. The only lioness who is in a good enough condition is vitani.
Kion and his group return. Without simbas approval they go to the elephant graveyard. Vitani is asked to stay to take care of the others in case the guard doesn't make it back.
Now in my version of the lion guard there are no super powers, no silly marks on their bodies. These are normal african animals. Kion would have mufasas traits and would be stronger than a normal lion cub on average but not super strength.
In a scene where we see the surviving hyenas talking, the little cubs try to escape. Knowing that someone will come to rescue them, from the shadows we see them being grabbed by the necks, having those necks snapped and having their dead bodies thrown atop a pile of bones. I do think this might be a bit too dark even for a pg rated movie. However I think this scene is necessary because I want a tearjerker that is not a complete retread of the mufasa death scene and boundry pushing for disney. Nobody expects two of the cutest lion cubs in the pride to be killed in a rather violent way.
The guard is able to fight off the hyenas well enough for them to surrender. While the guard is comprised of mostly young animals the hyenas were weakened by the previous fight to make the guard win plausible.
This starts the third act, because it's a disney movie it can't end on a downer ending nor does every movie need to end with a big action scene. It would be about the guard watching over the pride while it recovers. In this act we see kion and his guard out, patrolling the area as most of the lionesses have recovered enough to protect simba and kovu.
They see a lost little hyena cub, kion in his anger almost kills it but stops before attacking it, realizing that what he would be doing wouldn't bring back kovu and kiaras cubs. So the guard brings the lil hyena to the other hyenas in what I would hope to be the most emotional scene in any disney movie. They leave without a fight.
The movie ends with a very christopher nolan/hans zimmer-ish scene in which kion talks to the pride about how they will work to defend the pride while it recovers, juxtaposed with scenes from the near future and possible threats from the tv series (which i would change from disney jr to disney xd.
So yeah this is never happening

Why do we fall? So that we can learn to pick ourselves back up again.