We know from Luke 2 that each person (or, certainly, adult male) was required to register to his own town. We also know that Joseph travelled (with Mary) from Nazareth to Bethlehem so that they could be registered there:
3 And all the people were going to be registered, each to his own city or town. 4 And Joseph also went up from Galilee from the town of Nazareth to Judea, to the town of David, which is called Bethlehem, because he was of the house and family of David
--Luke 2:3-4 (AMP), emphasis mine
The common assumption is that everyone had to be at their ancestral home for the census, however the passage doesn't exactly say that. It states that people would be registered to their own city or town - presumably, the city or town they happened to be in at the time of the registration - and that Joseph went to Bethlehem because he was of David's line.
Since genealogy was so important to that culture, could it be that Joseph travelled to Bethlehem of his own volition to emphasise his ancestry on his official registration, as opposed to being required to go there by the authorities? Is there any evidence that people were required to travel to their ancestral homes as opposed to many Jews choosing to do so?
(By "evidence" I don't mean original documentation as that's obviously going to be pretty hard to come by; I'm really wondering if this has been discussed by subject matter experts and what conclusions, if any, have been drawn.)