I think its a very special bond between father and son to be nude together without the incest part. Walking around nude and hanging out nude and even hugging nude. I would think it a special bond. I've seen my father nude and even just his penis as he used to pee with the door open. He wasn't one I could approach and ask him to just look at it let alone touch it even though I had the desire to do so. My father was a sound sleeper and when I was 10 or 11 I used to sneak in his room at night and cop a feel. Did that for a while. When he fell asleep on the chair, I would put my hand on his crotch and feel around. It was nice only wished I could have done it when he was a wake but he wasn't approachable like that.
I remember him showing me how to stand up and pee when I was a kid, how he used to stand behind me and hold my penis showing me how to aim. He did that a couple of times until I got the hang of it. We grew apart as I got older as he became an alcoholic and abusive.
For fathers who want to bond with their sons and are able to go nude. A nude hug, penis touching penis shouldn't stop you. The penis should not be off limits after all its only a penis. Wouldn't you want you son to come to you if he has penile problems instead of suffering in silence or going to your son for help if you get hit in the balls. Have medical exams together be free to touch in a non sexual way. In other cultures, fathers and sons bathe each other including the genitals. To them its no big deal. I tell my friends both straight and gay that I'm touchable and if they feel the need to touch a dick feel free to touch me. However jerking me and sucking me off, then we have to talk. I guess I'm more free thinking because I'm a body groomer, I wax and/or shave men and the penis is not a big deal for me. Apparently not for them either because they're trusting me with their balls.