My guess for the reason that you don't see more manufacturers doing the single driver thing is that a large part of it is a marketing concern. It's a hard sell to convince the audiophile community that a single drive can give high quality sound and there is also a push for the widest possible frequency response to report on as well.
I converted to Omegas (Super 3XRS) earlier this year. Mentally it was a big step and truthfully, I don't think I could have done it if I hadn't gotten a chance to hear them before I took the plunge. After having lived with them now for 7 or 8 months, I haven't regretted the decision one bit.
What I get with my Omegas is a speed, coherency and a very unbox like sound with the best soundstaging and imaging capabilities of any speakers I've owned. I have two systems set up, besides my Omega Decware system, I have another that I rotate Kef LS50's and Harbeth P3ESR's in and out of. I have to say, it's hard to listen to the Kefs and Harbeths after listening to the Omegas. Both sound slow, boxy and very discontinuous. It's like you can hear the transition from the midrange to the tweeter and I also hear an odd phasiness with those speakers that the Omegas don't have. It's common for two way speakers to have the tweeters wired out of phase with the woofers and both the Kefs and Harbeths are designed this way. It's possible that I can now hear this after living with the Omegas. Before I owned the Omegas, I never even heard these colorations, now they jump out at me instantly. When listening to the Omegas I am often reminded of the sound I used to get with some Magnepans I used to have.
I think the true strength of the Omegas though is their ability to let you play them with some of the low powered SET amps. The advantages of the Omegas really shine through once you start to play them with these types of amps. With my Class D amp, my Omegas start to sound too lean, but they do sound better with a warmer Musical Fidelity integrated I have, but really, when I play them with either of my two Decware amps, the overall sound really differentiates itself from my other traditional system. It's been postulated that amplifiers with high negative feedback don't interact well with high efficiency speakers. My experience seems to support this.
That said, I can understand where the single driver concept isn't for everyone. Shortcomings of my system and I can easily live with them is that the sound ultimately isn't as big or with the impact of traditional speakers. After all, this is a single small driver and at the end of the day, it's not going to move as much air as a big multi way system. For me, it's not an issue, but for others, I could understand how it could be. I know some people play their music quite loud and for those folks, I'm sure some of them would miss some of the big sound you get from multiple driver setups. Also, ultimate bass response is limited. According to my SPL meter, in my room, my Omega's start to roll off right at 60hz. I'm not a bass freak so it's not a big deal and Louis makes speakers with larger drivers, so as you move up in driver size, this should be come less of an issue. Don't get me wrong, the Omegas will play loud and with impact, but if you are the type of person that blasts Midnight Oil with 100db+ peaks, you'll notice that they don't have the slam that a comparable well designed two way with bigger drivers has.
Good luck with your decision and let us know how it ends up.