I tried to build such a gimbal with Lego, but after making it solid, it becomes quite heavy.
On one of the Youtube films connected to the one you posted, somebody used plastic piping he glued together, so he could fim himself from ‘behind’.
I have another idea. Start with a backpack and make use of tubing that is used for heating and sanitary. It’s a combination of plastic and aluminum. Quite light, somewhat flexible, rather handy to work with.
So from the backpack I would create some sort of tripod going up. Then from there I would use nylon cord (3) down to a hula hoop ring. This ring might move/wobble somewhat, but it would be self stabilizing. For making pictures that would be good enough. For video, probably not.
The advantage of such a ring, would be it becomes possible to mount cameras/smartphones in more than 1 direction. I think I would let it come down to shoulder height. It can be used equally well on foot as by bicycle.
I agree with you, if you would think that it might look odd though… which is probably why I hadn’t made it yet, but now that the idea is becoming more concrete in my mind, it could happen any time. I’ve been toying with the hula hoop idea for a few months now, but I didn’t see how to make it happen, as I was considering to have it come down from shoulder height. Now I think it’s important to go up first, then have the ring at shoulder height. At waist height it would be bothersome for use on a bicycle.