Dragonball is a cult manga: fans are under alert and ready to voice their opinions in case they are not satisfied with the choices made for Dragonball the movie.
That's probably why we only have scarce details about Dragonball: the production does not want to suffer from a backlash....
Nonetheless so far the selection of the cast of Dragonball hasn't fueled any real controversy. After all it's not that bad and quite close to the characters of the original manga:
Piccolo's head is
still kept secret...
But should be close
to what you see.
Whatever the final movie looks like I think there will be something positive: at least this Dragonball movie is putting the spotlights of Hollywood on the great manga. Even if the movie does not transform into a great blockbuster we could hope that in the years ahead some equivalent to Christophe Nolan will reboot the franchise like he did with Batman!
But wait: Dragonball is probably gonna be a huge surprise and we won't have to wait for a reboot!