I am not totally opposed to it, I think its kinda funny but I dont think it should go on very long. ( not telling people which sex s/he is) I think that when you are trying too hard to make things neutral, you will inadvertedly start pushing the kid into the 'other' direction, just to make a point of how open and neutral you are. ( like a boy towrds dolls and a girl towards more boyish things ) I think its cool, as long as the parents are exposing the child into activities and toys both sexes would like, and are ok if their girl child turns out to be a total princess and girly girl instead of a rough tomboy or vise versa if 'its' a boy, but I have a feeling that in this case, they will push their child toward the things the childs opposite sex peers typically enjoy just to make a point.
I also dont care about their 'parenting' too much particular, where their older kids are left to make their own decisions of mostly everything, are 'unschooled' ( just learning as they go, no actual schooling or even homeschooling). I mean the other two are still young and could get a real education as time goes on but any parent who 'unschools' their kids thru life, has some parenting issues.
My boys had a doll (they asked for one I got them one ), my olders favorite color is red, middleones is pink, my daughter likes to play with cars and wrestle with her brothers, I think its important that you are exposed to all kinds of toys and activites but your sex is important part of you and I dont think keeping it a secret is doing anyone a favor. I think you should just take cues from your child, not force a girl into a dress or boy into football but they are making a bigger deal about being neutral than needs to be.