The most interesting aspect is probably the new power - ups. Since he still has his tail, there could be new forms related to it. Maybe a combination of his normal Super Saiyan forms and his ape - like abilities. It's exciting to think about how this would look in battles.
I think the most interesting part is how it changes Goku's character. Without losing his tail, he may retain some of his more primal instincts. This could lead to him having a different personality, being a bit more wild and unpredictable. And this new side of Goku would surely bring some fresh and unexpected plot twists in the fanfiction.
One of the most fascinating things about this fanfiction is how it impacts the Saiyan lore. In the original story, the loss of the tail was a part of Saiyan evolution. But here, Goku not losing his tail means that the whole concept of Saiyan growth and development has to be re - evaluated. It could open up new backstories and explanations about the Saiyan race, their powers, and their place in the universe. This re - imagining of Saiyan lore could be really engaging for fans who are interested in the deeper aspects of the Dragon Ball universe.