What an interesting thread, I have only had time to read the first half a dozen posts. I'll read the rest later.
I think I do 'some' of this unconditional parenting with my DD 2.4 years old. I frequently explain what we are doing and why. I have a hand sign and a phrase 'DD, In five minutes we are going to do x' Which I use to warn her that we are changing location and activities which seems to prevent issues.
I also give her many choices in her life. Interestingly my mum commented on how well (relatively for her age) that my daughter listens and responds to others. Then in the next breath critised me for listening to her when I asked my daughter to put her socks and shoes on in the house as it was cold and she declined and so I left it. I tried to explain to my mum that it wasn't an important issue and DD would ask for her shoes if she got cold and by listening and respecting her choices for the little things, meant she listened to me about the bigger things.
I am no push over and I do have some things I won't budge on, carseats, reins and/or holding hands outside the house, no biting or hitting.
I think having some control over their lives within flexible boundaries makes for happier secure children.
Which is why we went out yesterday with toddler dressed in top and jeans (I insisted on this base layer due to the bad weather) and my toddler still got a 'summer dress' i.e. a pink fairy dressing up dress, a yellow umberella and my old empty massive handbag to set her outfit off. Things like that don't matter and she still got to wear a dress which is all she wanted to do