Due to the fact that Christ was an actual person i find it to be intensely possible that there are people who share his bloodline.
Had there been more proof and less speculation, perhaps i would be more interested in finding these things out, because from what ive seen, many things involving Christ have been little more than a religious fanatic's personal speculation.
But as to how it would change Christianity, i doubt it would change much of anything. There are only two instances in which i can see a radical change:
1. Jesus had a child while commiting adultery
2. His descendant starts the second coming.