I think upright bikes will become more popular as vendors acknowledge the majority of people purchasing bicycles aren't planning on racing them or careening through forests.
Since I didn't get around to posting on this thread 2 years ago, I'll go ahead and do it now
I think upright bikes will get popular if and when more people start buying them. The vendors will be more than happy to supply the market with whatever it wants. The vast majority of vendors follow trends, they don't set them.