Primary Design Goals:
I bet you think that this looks like an ordinary monkey coffin speaker, do you ?
I can tell you, it is not. I would rather think that the speaker has potential (since I haven't listened to it yet) to become a wolf in sheep's clothing as it is full of features, which are a result of the following design goals but not necessarily visible at first glance:
1. Controlled and uniform horizontal radiation that is in agreement with psychoacoustics.
2. Controlled and relatively narrow vertical radiation to minimize floor and ceiling bounces in form of a real D’Appolito arrangement.
It is my opinion that more vertical control is not required.
3. Minimization of diffraction. The midrange drivers are operated below the baffle step and the tweeter most likely beams enough before it negatively interferes with the edges. If not, chamfers will help.
One baffle step (in the tweeter section this time) can never be avoided and has to be dealt with appropriately.
4. Placement of the woofer a la Allison (close to the floor) to avoid sound power response irregularities due to boundary effects between approx. 100Hz and 200Hz.
5. Separation of low end and mid/high frequency section at the typical Schroeder frequency of small rooms in order to address both operation modes of the room separately and systematically.
For the FR above the transition zone see 1. and 2.
With separate subs it is easier to implement more than one control mechanism in the modal region of the room as required (e.g. placement, low Q of the woofer HP behavior, DSP).
6. Max SPL has to be high enough for typical living rooms.
7. The speaker should be easy to build while being robust and somewhat nice looking (regular people don't understand plumbing pipes).
A housing without audible resonances and vibrations of any kind and minimizing re-radiation of sound through the driver's cones goes without saying. That is rather a prerequisite than a design goal as well as low distortion.