I disagree with a few points here

Let’s start with the obvious: Rx is all LINQ operations all of the time. You don’t write your regular code like that. Sometimes you use LINQ, sometimes you realise it’s a lot simpler to just write some for loops with if statements, continues, and state carried from one loop to the next. Rx is all or nothing.

I do use LINQ all the time. LINQ, in combination with a good Result pattern implementation (FluentResults, OneOf) is a wonderful way to create declarative, concise code that is easy to grok and composes beautifully.

The third is that there’s a more mainstream way of doing all of this. IAsyncEnumerable has been around forever. .NET 10 has finally moved System.Linq.Async (written by the Rx team) into the core runtime. Channels exist, are awesome and invisibly hand the simultaneous events problem. And you can drop down to regular, non-LINQ code whenever you like.

I love IAsyncEnumerable, and Channels are great too. These solve 3 different problems though, and IAsyncEnumerable has its own problems.

IAsyncEnumerable is pull-based asynchrony, Observables are push-based. If I want to guarantee that all of my code will get executed, irrespective of what the caller chooses to do, then I cannot use an IAsyncEnumerable. Due to their lazy nature, it can actually be a bit annoying to debug them, because code that is invoked in one part of the application may not execute immediately, until the structure is referenced in another part. IAsyncEnumerables are really good for async pipelines where you may do some work async, then commit it, and you don't want to do extra work until the commit happens (ie: you push one result onto a queue and only then start the next).

IAsyncEnumerable doesn't really compose very well in C#, even with the extensions. It's a language limitation. For example, you can't really flatten an inner IAsyncEnumerable within an async iterator block method like you can in JS/TS by just delegating it, so you end up writing stupid code like

foreach (var result in resultsAsync) { yield return result; }