> We are speaking about languages, not which implementations are available.
When it comes to adoption, an area where Eiffel has clearly lagged, the availability of implementations can't be an afterthought; not when you have good, free implementations for Python, Ruby, Go, Rust, Julia, and many more.
Objective-C and Swift are interesting languages that are held back by the fact that the best environment is Xcode on a Mac. Similarly, Qt has been plagued by license anxiety for years (first the QPL, and now the delayed LGPL releases). Therefore, I would say that one of the "obvious, non-negotiable things any new OO language should have," to quote the article, is a good open source implementation.