Some fanfictions have Naruto getting super powers as a result of a divine intervention. Maybe the gods or goddesses of the Naruto universe see his great potential and decide to give him additional powers to help him in his quest to bring peace. This can lead to all sorts of interesting plot developments, like him having to prove himself worthy of these powers to the divine beings or facing the envy of other ninjas who don't have such divine blessings.
Boruto could have visions or dreams that show him Naruto's past. Maybe he enters a forbidden realm or unlocks a secret power that allows him to experience his dad's history.
He might gain a more powerful form of Rasengan, like a Rasengan that can change its shape and properties according to the situation. Maybe he has better control over his Nine - Tails chakra and can use it in more creative ways without losing control.
There are specific storylines within the New 52 Flash series where Wally gets powers. These often involve complex plot developments and encounters with powerful forces.
He could develop the ability to combine his chakra with Superman's powers. For example, he might be able to use his Rasengan while flying at super - speed. Or he could infuse his chakra into his heat vision to make it even more powerful.
Maybe it's the high expectations that Naruto has for Boruto. Naruto is a hero, and he might unknowingly put a lot of pressure on Boruto to follow in his footsteps. Boruto could be scared of not being able to meet those expectations.