Jim,
I respectfully disagree with you on the merits of the "speakers to match the room" idea. Unless you happen to have an anechoic chamber for a listening room, you're always hearing a combination of the speaker and the room. Below 150ish hertz, you usually hear mainly the room. Tailoring the bass balance of a speaker to the room size makes a ton of sense to me. BTW, you often see a debate in these threads about bass balance for this speaker model or that. (I can't believe you like the Acme model XYZ, it has way too much (little) bass!). I always wonder what the poster would say if he heard the same speaker he's trashing for bass balance in a much bigger (or smaller) room.
As to your other point (Why aren't omnis more popular?), that's a good question. Here's another question:
Let's pick a # and assume that of the next 100 folks who visit Audiogon, 10 or fewer have heard omnis. If the other 9o were to audition a well designed omni (like Ohm or MBL), how many would want to switch. Certainly NOT all 90. But I suspect that a fair number would think hard about it. Why the market hasn't addressed that opportunity, I don't really have a good idea.
Marty