Don got his post in there while I was typing so I am echoing most of his post.
"I have seen a rash of monitors coming right out of studios. So would they have a market for a 15" based monitor or are we it???"
Well Rob, I think you nailed it. We are it.
I think it is pretty obvious that JBL would still be selling large format studio monitors if the studios wanted them. As Bo pointed out they still make some for the export market. If there was any real demand, they would still be selling them to studios here as well.
I was reading an article in Mix magazine a while back and they were interviewing some studio designers. In the section where they discussed the monitors they referred to "those large soffit mounted speakers that everyone hates". Apparently they prefer the small near field monitors produced by everyone including JBL.
TAD, Meyer Sound, and Westlake are all still making large format horn based monitors, but in current studio shots I see a lot more dome based systems from Dynaudio and others. The big horns with their inherent colorations don't seem to be in big demand. That is part of the reason we have so many to choose from on eBay.