All technical and sensationalist jargon aside...the simple ability to delay the mains, very easily accommodated in the multichannel or pro world to make life a whole lot easier...but, a freaking rarity in purist hifi.
@deep_333 In many rooms you don't need it, owing to the fact that the best way to do subs is with multiple subs so as to break up standing waves in the room.
Below 80Hz in most rooms (unless they are very large) the bass has bounced all over the room before your ear can sort out what the bass note actually is. This is because at 80Hz the wavelength is 14 feet. So its had time to bounce off the wall behind you and pass by you again before your ear can even tell the note.
If the note is cancelling the incoming bass note when it bounces, that is called a Standing Wave and no amount of EQ can fix it because the power you put into that result gets cancelled- you simply eat up amplifier power.
That is why multiple subs works so well- because if placed asymmetrically, they can break up standing waves so you get evenly distributed bass at the listening position as well as everywhere in the room.
So a time delay doesn't win you a whole lot in this situation.
Audiokinesis has a sub called the Swarm which is 4 subs each using a 10" driver. Because 4 subs might seem a lot to many people, they are designed to sit against wall to take advantage of the room boundary effect @mijostyn mentioned earlier. The subs are designed to roll off at 3dB/octave starting at 100Hz to compensate. This allows them to be flat to 20Hz in a compact package (1' square, 2' high). Because there are four 10" drivers, they don't need to have to have a lot of excursion unless the room is quite large. Because they are meant to be placed against the wall, they tend to be more innocuous; very easy to live with, not just in terms of space but also very easy to integrate into a system!