The Mother Flame is a substance created by Dr. Vegapunk, and utilized by Imu and the Five Elders. It is produced in a power plant on Egghead. It feels confirmed now that the Mother Flame is a fusion reactor, and thus practically a sun in a bottle.

Nika and Luffy in general are greatly inspired by different Asian monkey god myths, Hanuman definitely being one of them. There the biggest plot point is him literally eating the sun.

Gear 5 takes a tremendous amount of energy to keep going and what would be more energy than a fusion reactor in his stomach.

Luffy is currently one of the Four Emperors of the Sea and certainly an incredibly powerful pirate. He has continued to grow massively in One Piece, especially starting the Four Emperors Saga. Although Luffy is currently very strong, to face characters like the Five Elders, or even Imu, he still need one or two more boosts in strength.

Currently, Luffy in his Nika form has been shown to be constantly running out of energy, which is usually resolved later by eating food aka energy, but I believe right now Luffy’s Nika form isn’t his full power form but is actually a weakened version.

Luffy may just need to eat Mother Flame, a seemingly unlimited power source of similar capabilities to the sun. This may be the missing piece to Luffy’s power which may transform Luffy from the white Nika to a more orange full power Nika form.

Being sun powered would also explain why Nika is known as a sun god, as non of their powers are particularly sunny as off yet.

Mostly, I want this to be true just to see what wacky choreography Oda would conjure if Luffy got to fight with such a power up.