Wow, that is a lot of "what if's".
Most crosses are going to look exactly like a cross, so it will be a rare thing for someone to register a purebred-looking cross. And if they do, shame on them.
Regisration would obviously be optional, for those who are interested in tracing genetics and...
Many breeds of animals, when first being established, have a very limited number of individuals to use for a breeding population. Having an open registry at the beginning of your efforts is a very wise choice. Remember that even individuals that are not perfect specimens can make a genetic...