The passive radiators I sell, have only been available for a couple months. Most people take a considerable amount of time to plan and execute a design.
Also... the passive radiators let you make a box smaller because they don't take up the same volume as does a large port. They don't fundamentally change the box size required for a given driver. That is driven by the T/S parameters of the driver. The Tempest-X, in the latest version was a driver aimed at really large enclosures. Using passive radiators wouldn't change that.
A high output driver designed around a smaller box has some issues though. Lets take the Maelstrom as an example. If you try to use a ported Maelstrom, you will need at the very least an 8" diameter port. Put it in a 5 cubic foot box and tune it to 18Hz. You need a port that is about 70 inches long to achieve that. Obviously that is problematic in a 5 cubic foot box and the port will occupy 2 cubic feet of volume, forcing the box size up to 7 cubic foot internal. You also have all kinds of port resonances in a port that long. It is a bad idea to use such a port in any design due to the port resonances.
You can achieve the same tuning with two PR-18s loaded fully up with mass. They take little cabinet space, there is no difficulty of trying to physically fit the part in the enclosure and there is no out of bandwidth noise related to port resonances. That is why the PRs are a good solution. They offer the benefits of resonant systems without many of the drawbacks. This is especially beneficial for high output drivers because of the necessity of using large diameter ports that must get longer in a given size enclosure in order to maintain the same tuning frequency.
Also I'd point out. A small enclosure is always going to be problematic for high output/efficiency at low frequency. It is impossible to get around Hoffman's law. The size of the box really limits you at low frequency. Equalization is a nice tool but it can only be used so much. Subwoofers are only a couple percent efficient and most of the power put through a sub is given off as heat (in the coil). If you have to heavily equalize there is only so far you can go before you hit thermal limits. Also the cone area & swept volume necessary for really high output at low frequency runs counter to small box sizes. It requires larger drivers with more stroke, neither of which lends itself to small boxes.
