I don't deny the utility of Rails for building a certain class of web site. But I think there is a difference between Rails and Ruby, and a difference between use of a technology and improvements to that technology.

I think a technology must continue to change and adapt to remain relevant. I see Shopify as the main driver of current improvements to Ruby (the core features of the most recent release, and the upcoming release, were mostly due to Shopify as I understand it). I don't see smaller companies doing these improvements and I think without them Ruby will (slowly, because it's used in some big places) fade away.