I'm not sure if it's extremely popular. Some fans might be into it, but it's likely a rather niche part of the Naruto fanfiction world. Naruto has a vast range of fanfiction topics, from epic battles to character relationships, and while foot - related fanfiction exists, it probably doesn't have as large an audience as more mainstream topics like Naruto's journey to become Hokage or his relationships with Sasuke and Sakura.
Yes, there might be. The Naruto fandom is quite large and diverse, so it's possible that some fanfiction writers have created stories where Naruto is seven feet tall. You can try searching on popular fanfiction websites like FanFiction.net or Archive of Our Own.
One possible plot could be that Naruto's sudden increase in height gives him an advantage in battles. Enemies might be intimidated by his new imposing stature. For example, in a fight against a powerful villain, his height could make his punches more powerful due to the longer reach.
The difference between seven, eight, and nine foot billiard tables was mainly in size and the place where they were used. Seven feet, eight feet, and nine feet were the standard size of a billiard table. The seven-foot billiard table was usually used for nine-ball play and was relatively small. The eight-foot billiard table was suitable for a four-meter-long room. It was suitable for small billiard rooms or places with limited space. The nine-foot billiard table was larger than the eight-foot billiard table. The stability of the table was better, and it could accommodate more players and referees. It was suitable for larger venues. Therefore, the choice of a seven, eight, or nine-foot billiard table could be decided according to personal needs and the size of the venue.
The main distinction of porn with a story genre from regular porn is the presence of a coherent narrative. Regular porn often jumps straight to the sexual action, while the story genre tries to add some kind of story framework around it. But in the end, both are adult-oriented and feature explicit sexual content.
One great Naruto and Happy Feet fanfiction could be 'The Ninja Penguin Adventure'. In this story, Naruto somehow gets transported to the world of Happy Feet. He teams up with Mumble and they go on a journey to save both the penguin colony and Naruto's village from a common threat. It's really interesting to see how Naruto's ninja skills blend with the penguins' unique abilities in this fic.
In some fanfics, a plot twist could be that the villain in the Naruto world is somehow related to the problems in the Happy Feet world. For example, Orochimaru might be the one causing the fish shortage in the penguins' world. It completely changes the dynamic as Naruto has to not only deal with his own world's issues but also those of the penguins.