Well, it's a rather strange concept. In the Harry Potter world, there's no established 'blood elemental' concept in the original canon. But in fanfiction, anything can be created. Some might find it interesting as it adds a new and unique twist to the familiar Harry Potter universe. However, others might think it goes too far from the original essence of the story.
Yes, it could be. Fanfiction often takes the existing world of Harry Potter and bends it in different ways. The idea of 'blood elemental' might seem out of left field, but it could potentially open up new storylines and character developments. For example, it could explore a new form of magic related to blood that was previously unthought of in the official books.
It's hard to say for sure. While fanfiction allows for creative liberties, the 'blood elemental' aspect might be a bit of a stretch for some fans. If it's well - written, it could be an engaging addition to the vast array of Harry Potter fan works. But it also runs the risk of being too far - fetched and not in - keeping with the overall feel of the Harry Potter series.