Not the person you replied to, but OCaml, Scala, and F# all suffer from the potential drawback of being functional-first, and thus difficult for people to adapt to. If you are someone who is an OO programmer and are considering Rust for its potential performance and different model, it would be hard for me to recommend a language whose model is as different as OCaml's. Learning Rust entails learning the borrow checker and unlearning some of your OO habits; learning OCaml requires a sea change in your whole mentality & approach to programming if you've never experienced a functional lang before.
Meanwhile, both D and Nim have the benefits of being procedurally grounded, and hence more familiar to someone coming from (say) C# or Java.
Having said that, I think both of those languages may suffer from a lack of tooling/library breadth & depth. Nim in particular seems really cool, but it seems to be struggling to catch enough attention & interest to build a larger community -- probably in large part because it targets many of the same people who are currently high on Rust.
I don't really agree here, even if they're not used much by the community OCaml can be written as a regular procedural or OO language. There are a few thing that can look weird for people new to this (immutable by default, the type system) but they're precisely what people looking for a GC'd Rust want I think. Rust also takes a lot from functional languages, and idiomatic Rust code usually looks like functional code. I think the biggest shock coming from Rust to OCaml would be the compiler errors and the quantity of online resources. There's a world of difference between the two, and they matter a lot when learning. I think the same is true for Scala. I don't know if F# is the same but since it takes from OCaml it may still have the procedural capabilities, and it seems it still has the OO features of OCaml.
I do agree that D and Nim may be easier to approach from C# or Java, or even Python for Nim or C and C++ for D. These already represent a huge chunk of programmers, but not really what the typical person looking for a "garbage collected Rust" is, in my opinion. Especially since Java and C# programmers already have Scala and F#. While they're both different from what they're used to, they leverage the same plateform and can use the same libraries which is a huge plus.
I agree with your conclusion too, and I think OCaml suffers from this too. Scala and F# have at least the libraries part covered.
Meanwhile, both D and Nim have the benefits of being procedurally grounded, and hence more familiar to someone coming from (say) C# or Java.
Having said that, I think both of those languages may suffer from a lack of tooling/library breadth & depth. Nim in particular seems really cool, but it seems to be struggling to catch enough attention & interest to build a larger community -- probably in large part because it targets many of the same people who are currently high on Rust.