While responding to another post, I was reminded of the Dutch and Dutch 8C. They address the issue in a different way:
1) They use mainly acoustic methods to present an out-of-phase "midrange" signal at the sides, to cancel the midrange as it is "wrapping" around the cabinet. Quotes around midrange as it will be frequency controlled. This would replace acoustic treatment with a traditional speaker.
2) They accept boundary reinforcement in bass frequencies and provide DSP correction, something that can be done with any speaker.