Boruto has the ability to use the Rasengan, which is a very powerful jutsu. He also has the Jougan, an eye power that gives him unique abilities like seeing chakra and some kind of predictive vision.
Their powers could actually be beneficial in some ways. Boruto's ability to think on his feet and use his various skills could help in solving some past problems. Himawari's Byakugan could be used for reconnaissance in dangerous situations in the past. But they must always remember that any use of their powers could have a butterfly effect. So they would need to be cautious and consult with each other before taking any major actions with their powers.
Rimuru Tempest has a wide range of powers. One of his main abilities is the power of Gluttony. This allows him to devour almost anything and gain knowledge or abilities from it. For example, he can devour monsters and acquire their skills, which makes him extremely versatile in combat.
Boruto could be developed by showing his growth in responsibility. For example, in the fanfic, he could take on the task of teaching Himawari a new jutsu. This would not only show his skills but also his patience. Himawari, on the other hand, could be developed by showing her becoming more independent. Maybe she decides to go on a small mission on her own to prove herself to Boruto.
A common power in fanfiction is enhanced magical senses. Characters can sense magic from far away, like being able to detect a hidden magical artifact from miles away just by the faint magical aura it emits. This helps in treasure - hunting type of storylines.
Loki, the God of Stories, has the power of shape-shifting and can assume various forms. He's also highly intelligent and skilled at deception and manipulation.
One idea could be a story where Himawari discovers a new ninja technique and Naruto helps her perfect it. They could have training sessions together, and Naruto shares his own experiences from when he was learning new jutsus. This would strengthen their bond as father - daughter and also show Himawari's growth as a ninja in - training.
Well, their child might inherit Naruto's chakra control and Shion's unique spiritual powers. Maybe the child could have an enhanced form of the Rasengan, combined with Shion's ability to predict the future in a battle sense. For example, being able to foresee an opponent's moves just a split second before they make them and using that knowledge to adjust the Rasengan's trajectory for a more powerful and accurate attack.
If Naruto had Kryptonian powers, his strength would be off the charts. He could do things like punch through solid rock without breaking a sweat. His durability would also be enhanced, so attacks that would normally harm him would have little to no effect.
His speed and strength could increase. Shinigami powers might give him a boost in physical abilities as they are often associated with otherworldly strength.