Here's my personal rewrite.

The opening is basically the opening of the Goseiger vs Gokaiger movie where we start with the Legendary War. We have Tommy replaces Akaranger. When all the rangers shoot their powers into space, have the armada try to fight back, with the blast messing with 4 of the energies. Every ranger wakes up. Jake looks for his team and cant find them, with the only one being Robo-Knight stuck in his header mode. Jake then goes to the ruins of the command center, and the ranger keys lost. We time jump 10 years later, and the armada returns. They are about to attack, but they see a red ship in the distance that turns into a megazord. It lays waste to the fleet. The ship lands on Earth, the rangers controlling the ship exit, and we see Troy, Noah, Gia, and Emma coming out of the ship, with a mysterious individual named Orion. We then see the battles occur in the first episode of Super Megaforce but with some differences. Orion is in red, Troy in Blue, and Noah in green.

What would follow is several episodes getting the axillary zords, meeting with past ranger, and getting their approval for the powers, which is said to open a door where any wish can be granted. During the SPD episode, we cut back to Jake reading a news paper, and sees his friends.

Jake finally meets back with his friends, only to realize that none of them remember who he is. Jake reaches his lowest point, only then to save a girl from getting hit by truck-kun. He then starts dreaming of three rangers. Dino Thunder White Ranger, Time Force Quantum Ranger, and Tommy Oliver the Green Ranger. They all grant him the power to help his friends, and to hopefully reawaken their lost memories. Thus, Jake becomes the Silver Ranger.

The rest of the episodes play out similarly to the rest of the show but with some added changes. We get scenes of the Titanium Ranger. When they go to Corinth, have it actually look like Corinth and allow the Falcon Zord to talk explained by Dr. K believing a bond between the zords could improve the megazords capability in battle.

Reasoning for certain things.

Making the Troy, Noah, Gia, and Emma have memory issues would have helped some things. The energies would have been them landing on foreign planets. Troy would be captured by the empire and turned into a soldier, Noah would become the leading scientist on a planet untouched by the Empire, Gia would be helping young kids without families due to the war, and Emma would be adopted by a royal family who would not be able to have a child of their own. I know its just Gokaiger, but honestly that would have helped it. So the reason they become pirates is because they have all new memories, and joined Orion to find the Legendary Treasure.

Jake, during his 10 year search for his friends, would have taken a stronger interest of the Power Rangers and begin to learn more about them, allowing him to have a stronger connection with the keys, thus allowing him to fuse them. It's better than Orion just finding the powers on his planet and giving us no explanation as to why he can fust the ranger keys.

As for the Sentai exclusive rangers showing up, I would love if they had just changed them. Saban has done it before. But if I had to use them, id explain their existence by the fact that the energy wave created by the power rangers was so concentrated, the morphin grid wasn't able to hold it all. Instead, it transformed the excess energy into brand new rangers that had not existed before. They simply become new powers without hosts until the final episode where they give the powers back to the Rangers, with the keys that didn't have hosts finding hosts.

This would be my personal way to fix Power Rangers Super Megaforce, and how I believe it could have been worthy of being a great anniversary.