He might have lost his main means of casting spells. This would put him at a great disadvantage in any magical battles or challenges. Without his wand, he would have to rely on other forms of magic or his natural abilities, which could be much more difficult.
Perhaps it was related to some new and untamed magical ability within Harry. For example, if he discovered a hidden power within himself that was too much for his wand to handle. His wand, which was made for normal magical use, couldn't withstand the intensity of this new power, and thus shattered.
He might face backlash from his own side. His family or the other Death Eaters, if it's set in that kind of context, could view his act as betrayal. They would likely be angry with him and might try to punish him in some way.
He might choose a phoenix feather because it represents rebirth and magic. And for the wood, perhaps he'd pick holly, which is often associated with protection in the wizarding world.
He might choose holly. In the original series, Harry's wand has a holly wood. Since he's making his own in this fanfiction, he could still be drawn to it for its traditional associations with protection and courage.
If Harry Potter snapped his wand in fanfiction, it would be a huge turning point. Maybe he'd start a journey to repair it, like finding some ancient magic or a powerful wizard who could fix it. Or he could discover latent powers within himself that didn't rely on the wand. It would be a great opportunity for the writer to explore different aspects of Harry's character and the magic world without the typical wand - based magic.
In fanfiction, if Harry Potter snaps his wand, he might lose a great deal of his magical power. His wand is his primary tool for casting spells, so without it, he'd be in a very vulnerable position. He could start to explore alternative forms of magic or seek out a new wand, perhaps through some extraordinary adventure. This could also lead to him relying more on his friends and the skills he has developed outside of wand - based magic.
One consequence could be that his relationships change. His friends might not recognize the new 'soul - changed' Harry at first, leading to some initial confusion and distance in their friendships.
One consequence could be that Harry feels an internal struggle. Since he has a part of Voldemort's soul in him, he might have to constantly fight against the dark impulses that come with it. For example, he may find himself having more aggressive thoughts or being more easily influenced by dark magic in certain situations.
The Death Eaters might think they've won at first. There could be chaos and fear among the good wizards. But it could also lead to a secret resistance growing stronger.
If such fanfiction exists, it may lead to a lot of negative impacts. It can mislead some young and inexperienced readers into thinking that abnormal relationships are acceptable. Moreover, it might face legal issues in some cases as it violates ethical and moral boundaries. Also, it will be shunned by the vast majority of the legitimate Harry Potter fandom who uphold the positive values of the series.