I think the main point of the article isn't exactly "monads are feasible in Rust", but rather, "monads are a viable motivating case for these potential developments in Rust". The author is on the Rust compiler team and has several posts from similar angles.
> Pretty misleading to write "... I want to demonstrate that monads are feasible in Rust." if that's not actually the case
When not taken out of context, I don't think it's misleading at all.
> You see, there’s a problem with talking about whether monads would be useful or not, and it’s this: there are a large number of design challenges to overcome to have any hope of implementing them at all — to the best of my knowledge, there currently exists no realistic (that is, practical) design for monads in Rust. In fact, there are so many obstacles that some people express doubt that it’s even possible.
> In general, I don’t think it’s worth talking about the virtue of a language feature if we think there’s no way we could actually implement it. However, I think there are arguments to be made in favour of higher-level abstractions in Rust. Thus, to facilitate discussion, I want to demonstrate that monads are feasible in Rust.
There's no discussion of implementation, we have no idea how "reasonable" an implementation would or wouldn't be. My assumption from reading this is it would require a ton of non trivial additions to the type system
