Is there consensus that we'll probably only get about 6K miles range on a set of 4?
None of us know. The only data point we have to go on is that one of the Roadshow cars with apparently about 6K miles looked like it needed new rubber in a photograph, and perhaps one person's observation. Of course the Roadshow cars will have led the worst possible life for tires since they will not have been driven normally, plus we really don't know anything about the tires on that one car; if 6K was really all they had on them, if the photos that people were looking at were giving an accurate read, or anything else. It's all speculation at this point.
Based on my experience with other vehicles sporting soft summer rubber, and the fact that the Karma is very heavy, I don't *expect* great tread life, but personally I would be surprised if the real number wasn't closer to 10 or 12K. We'll all find out as soon as a few real owners with real world use rack up meaningful miles.
On my previous car, and MB SLK55 AMG, the Michelin OEM rubber was horrible and didn't make it much over 10K, and I got a lot better life when I switched to Goodyear Eagle F1s, so I don't know that just comparing brand names tells us much.