If you read the most recent article posted about BF, you'll remember some of his comments about the NFL vs college ball. It seems his heart is in the college game. He also had some interesting comments about getting to know his dad better after playing for him. It's not such a stretch. If his goal is to be a HC in the NFL, he'll stay put with very, very good reason. If he loves the college game, the OLine coaching spot seems ideal.
I will say if KF hires Brian, I'm sure it won't happen without a ton of conversation and introspection. I just don't see KF putting his kid in a position to fail or be heavily criticized. If he hires Brian, it's on his own merit.