I am been doing some pretty intense research dipole and IB sub design. I have built just about every box known to man except dipole and IB over the last 20 years. I have done TL, Bandpass 4 and 6 order, bass reflex, EBS, isobaric, isobaric bandpass and many more.
But I am studying dipole because of the way in which it interacts with the room ie the lack of room modes. My question is this,if ones was to take two EBS "LLT" subs and put them back to back out of phase wouldn't this create the same effect as a dipole? In other words it would not excite the room modes to the bottom top or side so the enclosure due to the null that the out of phase drivers would create; like the image below shows. This should work right and give the best of both worlds. Great transient response due to the lack of room interaction and the q and speed of a sealed box with the low-end of a bass reflex. Or is it just late and I am off my rocker?
Calculate Room Modes 