I think that if your kitten was used to a lot of kitties around and then went to an only pet home, he might simply be unsure about this...in which case, another kitten will give him more confidence.I should add that Im looking into getting an F2 and am waiting for the babies to be born. Different breeder...good or bad idea? Since we have this issue.
I don't think it will be a bad thing, either he will remain less social (and you will have the other kitten for that affection) or he will improve seeing your interactions with the hopefully more social kitten.