Originally Posted by Charlatan

If I remember correctly we'd been dating for about three years and had only lived together for about four months when I asked her to marry me (and I am not sure if her parents knew that she'd moved in with me at that point).

I too have an excellent relationship with my wife's parents (perhaps even better than my own parents at times). I still wouldn't ask permission. To me, the symbolism of the act is enough to infantilize her. Your scenario would infantilize me and commodify her.