The creator has been consistently clear in his take on "Why Nim?" It's a general purpose systems programming language, favoring procedural style, that's superior (or aims to be) in a variety of ways compared to whatever else you've been using. Hubris? Maybe.

In practice, it's turned out to be an "expert's tool" that's more expressive-convenient than C/++ to do all manner of things in the realm of systems programming, from embedded to HPC. And it's got great C/++ interop, so you can continue to leverage those software ecosystems.

In that respect, I'd say the biggest boon, rather than a killer project, would be for a famous programmer or shop to publicly and loudly adopt it as their everyday language, shouting its name for several years and saying things like "Wish we had started using this years ago, would have been so much better, look at all of these great apps and libraries we've been able to create and maintain more easily than if we'd stuck with C/++/Go/Rust/Swift!"