I can see how this works, but my personal experience is that concurrent code that is finely scoped is easier to reason about than larger-scoped concurrency already anyways. Hardly a controversial statement, I guess. So if nurseries help me reasoning about finely scoped stuff even better that's great of course, but only solves part of 'the problem'. And maybe not the most interesting part.
Just quickly running a task to perform a handful of stuff concurrently for a single purpose (like doing a few network requests and packing the results) is hardly where I encounter big issues. The compositional behavior of Futures really helps here I think. A bunch of `Future<Result<A, Error>>` go a long way.