While not "boxless" in the literal sense of the word, omni-directional and poly-directional designs often have a presentation reminiscent of an open-baffle or planar speaker. I believe that much of what a good open-baffle or planar speaker does well results from the relatively late-arriving backwave energy, and essentially the same effect can be generated by other techniques, some of which offer advantages in efficiency, bass extension, or dynamic headroom.
How many 'listen outside of the box' design?
Whether I owned electrostats or open baffle designs the majority of my audio life I've owned boxless speakers. My choices were made in part due to a logic of removing a 'box' from the equation of having to interact with a room. The more I thought about it it seemed a very logical choice. Why enter a speaker into a box and then have to deal with the resonation of the speaker interacting with the box and the room? I'm not saying successful box designs haven't been built, what I'm suggesting is box designs seem a more complicated way to achieve true room integration. I've discovered, dollar for dollar, I've exceeded most box designs. How many think as I do, or have experienced similar results based upon experimentation?