It has many fans, probably because there is a lot of tension between them, they don't really get along and that makes the pair really interesting.
It wouldn't be a surprise if the couple becomes canon, because, apparently, all members of the Hyuga clan have the byakugan ( males and females) and that means...
Yes. Arranged marriages between family members. They have to maintain the bloodline.
This pairing is actually one of the most popular in Japan (Following NaruSasu and NaruSaku) where as in the US its not so much due to western ideas on endogomist (or incestual) marriages.
Hinata and Neji are blood related and are considered to be close cousins. Some may argue they are too close due to their parents being twins. This, however, does not change the relationship between these two being cousins. In other words they wouldn't be labeled "half-siblings" just because their fathers are twins. The genetic make up (DNA) even among identical twins are still slightly different.
Warped ideas about genetics from western thinkers tend to work against this pairing alot. But very devoted fans never pay mind to this and continue loving this pairing regardless.
This pairing could be possibly canon due to their clan's upbringing but if it actually does it would only be slightly mentioned at the end of the manga (unless Kishimoto feels like being a Hyuuga fan again)...since this manga is not really about them as ma...