Unfortunately, Go also made their channels worse by having their nil semantics be complete lunacy. See the "channel API is inconsistent and just cray-cray" section in the article.
But there are a couple of problems I can think of.
The first is over-scoping: a structural interface is matched by everything that appears to implement it. This can complicate refactoring when you just want to focus on those types that implement a "specialized" form of the interface. So, the standard library's Stringer interface (with a single `String() string` method) is indistinguishable from my codebase's MyStringer interface with the exact same method. A type can't say it implements MyStringer but not Stringer. The solution for this is dummy methods (add another method `MyStringer()` that does nothing) and/or mangled names (change the only method to `MyString() string` instead of `String() string`) but you do have to plan ahead for this.
The second is under-matching: you might have intended to implement an interface only to realize too late that you didn't match its signature exactly. Now you may have a bunch of types that can't be found as implementations of your interface even though they were meant to be. If you had explicit interface implementation, this wouldn't be a problem, as the compiler would have complained early on. However, this too has a solution: you can statically assert an interface is supposed to be implemented with `var _ InterfaceType = ImplementingType{}` (with the right-hand side adjusted as needed to match the type in question).
I really doubt this comes up in smaller, one-team repos. But in the coding jungle I often deal with, I spend much more time tracing code because of this issue than I'drefactoring. Make no mistake: I like Go, but this irks me.
I think this article on channels suffers from "Seinfeld is Unfunny" syndrome, because the complaints about channels have largely been received and agreed upon by experienced Go developers. Channels are still useful but they were way more prominent in the early days of Go as a solution to lots of problems, and nowadays are instead understood as a sharp tool only useful for specific problems. There's plenty of other tools in the toolbox, so it was easy to move on.
Whereas, nil is still a pain in the ass. Have any nontrivial data that needs to turn into or come from JSON (or SQL, or XML, or ...)? Chances are good you'll need pointers to represent optionality. Chaining structVal.Foo.Bar.Qux is a panic-ridden nightmare, while checking each layer results in a massive amount of boilerplate code that you have to write again and again. Heck, you might even need to handle nil slices specially because the other side considers "null" and "[]" meaningfully distinct! At least nil slices are safe in most places, while nil maps are panic-prone.
As the author of the post, it's really gratifying to hear that this is your assessment nowadays. I agree, and while I'm not sure I had much to do with this turn of events (it probably would have happened with or without me), curbing the use of channels is precisely why I wrote the post. I felt like Go could be much better if everyone stopped messing around with them. So, hooray!