I probably wouldn't breed the dog because shyness is not a desired trait.
I guess it would depend on what I was breeding for and if the pros outweighed the cons. I mean, if it was back in the day and the dog was game as game got, then ya, I'd breed. If it was a working dog for the farm and the dog worked from sun up to sun down, then ya, I'd breed. If I was breeding for sports, then no. I really don't know how great a shy dog would be in sports.
So, I don't know. It would depend on what I was breeding for and what the dog had to offer. If I thought that the shyness could be overlooked based on other traits, then yes. If the other traits were not strong enough to justify the breeding, then no.
This is all hypothetical, right?