What's limiting the growth of Nim in my opinion isn't the ecosystem; I believe the ecosystem grows with the adoption (and not the other way around).
On the other hand, successful languages usually have 2 things that Nim is currently lacking : * No big-name organization (Rust has Mozilla, Go/Dart have Google) means people are not sure they can trust the language or its stability over time. * No "killer-app" to showcase what you can do. Basically it's marketing a solutions instead of a tool (even if the distinction isn't that important from a technical perspective). I'm not saying it is easy though, especially for open source projects.
