Very interesting to think about. I'm not sure that any one manufacturer has really gone all out and put together everything that would be possible in an advanced cabinet for a dynamic box speaker. Some things do readily jump to mind. The first cabinet design I remember really capturing my attention was the original B&W Matrix, and their idea for internal reinforcement was widely imitated, but not to same complete degree as they employed. B&W also popularized the "bullet" tweeter with no baffle. Thiel has been influential with their concept of a smooth baffle curving away from the drivers without sharp corners, and also a grillecloth frame that integrates with the surface to avoid interupting it. Vandersteen and Dahlquist emphasized minimizing baffle size, and Dunlavy applied damping material to the baffle around the drivers. Alon mounted drivers on a "cabinetless" free baffle open to the rear. Wilson uses dedicated advanced composites for their enclosure panels instead of the ubiquitous MDF, and made many models with separate cabinets for the different drivers. Kharma has created a fascinating cabinet with a contoured interior surface designed to diffuse sound waves. Gallo made speakers with 360' symetrical spherical cabinets of spun aluminum. Many makers have tried to reduce or eliminate parallel cabinet surfaces, use thick baffles, use internal sub-enclosures, and brace internally at the very least. Likewise, many have designed slanted baffles to help with time-alignment, and many have gone to symetrical, "D'Appolito"-style speaker arrays to mimic a point-source, or to multi-driver columns designed to mimic a line-source.
I don't think it's possible to choose just one type of cabinet loading, i.e. sealed, reflex, tansmission-line, etc. as being unequivocally better than the others - a good (or bad) design could be made with any of them. But I do think that the traditional preponderance of speakers on the market following the status-quo of rectangular, square-edged cabinetry made from MDF will fade away. Although plenty of good designs have been made this way (and still are), I think the bar is being raised, albeit slowly. A big manufacturer like B&W obviously has the edge when it comes to the kind of resources needed to inovate a remarkable design like the new Nautilus midrange enclosure, with its elongated semi-spherical, quasi-transmission-line, all-synthetic, baffleless cabinet (and still sell it at a reasonable price, to boot!). But I believe computer-aided design, and the demand for ever-better sound, have numbered the days for makers who don't take the next step in trying to reduce or eliminate addressable problems with conventional cabinets, such as resonance, flexing, standing waves, diffraction, reflections, durability, and the like. There's still a lot of room for overall industry advancement in the area of speaker cabinets, utilizing superior technology and materials, but audiophiles will probably have to get used to a different kind of appearance and a likely a higher price.
