There could be a plot where Harry Potter as the Sorcerer Supreme has to interact with other powerful magical beings from different dimensions or realms. He might have to use his enhanced powers to protect the wizarding world from threats that come from outside their normal scope of knowledge. This could lead to all sorts of exciting adventures and challenges.
I think it has the potential to be good. It combines two very cool concepts - Harry Potter and the Sorcerer Supreme. However, the quality can vary a lot. Some fanfiction writers do an amazing job of weaving a new story within the existing Potterverse, while others might not be as skilled.
One possible plot could be that after the defeat of Voldemort, the magical world is in a state of flux. Harry, in his search for a way to further secure the safety of the wizarding world, stumbles upon the ancient power of the Sorcerer Supreme. He then embarks on a journey to master this power. Along the journey, he meets old friends who have different reactions to his new path, and he also uncovers a conspiracy within the wizarding world that wants to use his new power for their own dark purposes. As he grows in power, he has to make difficult choices about how to use it and who to trust.
Obviously, Harry Potter would be one of the main characters as it's in the title. He would be in the role of the Sorcerer Supreme. Hermione and Ron would probably still be important characters, supporting Harry in his new role and adventures.
The plot might involve the Sorcerer Supreme realizing the great potential in Harry Potter. He could start by teaching Harry basic magical control in a very different way than normal. As Harry grows, he gets involved in the Sorcerer Supreme's battles against other magical threats. This gives Harry a broader perspective on magic. When he has to face Voldemort, he uses his unique training and knowledge to outwit the Dark Lord in ways that no one expected.
One interesting plotline could be Harry Potter somehow inheriting the title of Sorcerer Supreme. Maybe he discovers ancient magic that links him to this powerful position and has to learn new spells and face new enemies. For example, he might have to deal with dark wizards who are after the power associated with the Sorcerer Supreme.
There are fanfics where the roles are reversed. For example, in some 'Harry Potter Sorcerer Fanfic', Hermione becomes the main target of Voldemort instead of Harry. This completely changes the dynamic of the story and shows a different side of how the wizarding world would react. Hermione has to use her vast knowledge of magic in new and dangerous ways to survive. It also shows how Harry and Ron would step up to protect her, creating a different kind of friendship bond.
Yes, it can be quite popular. Combining the world of Harry Potter with the concept of the Sorcerer Supreme, which is often associated with Doctor Strange in the Marvel universe, creates an interesting crossover. Fans enjoy exploring how Harry Potter's magical abilities and world could interact with the idea of being the most powerful sorcerer, like the Sorcerer Supreme.
Obviously, Harry Potter is one of the main characters. Since it's about him as the Sorcerer Supreme, he would be central to the story. Hermione and Ron would likely also be important characters, supporting Harry in his new role and adventures. They might help him research about the powers and responsibilities of the Sorcerer Supreme.
One common theme is power expansion. Harry is already a powerful wizard in the original series, but as the Sorcerer Supreme, his powers are enhanced and he has to learn to control them. Another theme could be cross - universe encounters, like meeting characters from the Marvel universe where the Sorcerer Supreme concept originates.
Well, perhaps in this fanfiction, the Grand Sorcerer is actually from a different magical dimension and he brings with him new spells and ways of magic. For example, he could introduce a new form of transfiguration that is more powerful but also more dangerous. And he might have a connection to the founders of Hogwarts that no one knew about, which could lead to all sorts of revelations about the school's past and future.