IMHO Eiffel's concept of simplicity is rather similar to what golang is aiming at today. It didn't serve Eiffel well.
Eiffel has generics, value and reference types, design by contract, non nullable references, pure OOP in Smalltalk linage, agents, it is designed for IDE based tooling, since the beginning had a mixed mode development workflow (VM inside the IDE and C or C++ compilers for release mode), uses dynamic loading for extensibility,...
The only thing that killed Eiffel in the mainstream was the target audience of Eiffel Software, basically enterprise with deep pockets delivering projects in areas where Eiffel capabilities are relevant.
The fact that Eiffel Software remains in business, kind of proves that there are enough companies willing to pay for such tooling.
Do you know different?
My last commercial Smalltalk was Smalltalk/V, just before Java got released, so not much I can state here.
Where-as for some reason I seem to imagine Pharo classes have been re-organized to use traits?
Any details why he thinks that way?
Same type of thing killed Ada in the mainstream.
NVidia has adopted Ada/SPARK for security critical firmware, for example.
Likewise, Genode is now replacing C++ with Ada on the security critical OS layers.
Eiffel had similar issues that Pascal had: Appearing too much like an educational, purist language and having "good enough" more popular alternatives on the market (C/C++ vs. C++/Java).
And authors that don't compromise to sell stuff.
The crappy "SmallEiffel" situation didn't help either. It started out pretty great (good feature set, quick and cross-platform compiles via C), but then, erm, FOSS nature took its course. Which is why I'm a bit ware of similar language and their situations since then, e.g. Nim.
Man, there was a time in the 90s where I was hoping that we'd get Eiffel (or Sather) as the next big open source desktop language. Instead we still have walled garden C++ and reinvent-the-wheel C.
The RESF might take issue with that statement. Though it was of course largely true as late as the 2010s, not just in the 1990s.
Right now not enough hubris for either Go or Rust to do a build their own thing right from scratch.
That said, that was about the time I started realizing just how pointless it is to learn niche languages, as anything other than an amusement. I can't recall the wording, but trumpet players have a saying that you can learn flugelhorn for fun, but trumpet is always going to be what pays your bills.