I really don't think "the goal was a bit too ambitious." I think they figured out that allowing people to use Macs to develop fantastic Windows software was not going to sell any more Macs.
Yellow Box for Windows was simply an incremental upgrade to OpenStep, a product which was released and worked perfectly well once-upon-a-time at NeXT. I'm sure Apple still has it working somewhere in the basement at Cupertino. Who knows, someday if there is ever a good business reason to release it, maybe they will. Personally I hope so.
But to suggest that the goal was somehow technically "too ambitious" is to ignore the fact that it was essentially already done. It was just a business decision.
I too thought the article's omission of C# was curious. I think Mac people have been "thinking defensive" about Microsoft for so long, they dismiss the idea that they might invent something good. C# as a language, and .NET as a runtime environment, are really quite excellent technology. The runtime is not as dynamic as Objective-C & Cocoa, but it more than makes up for it in terms of shallow learning curve, excellent (albeit not free) developer tools, and support for many languages sharing objects transparently. You people complaining about Microsoft "bastardizing" languages with .NET, you really need to study it a bit--hey, even try using it--because your criticism sounds suspiciously uninformed.
I would really be surprised if Apple didn't have at least some plan up their sleeve to take advantage of .NET languages and architecture in a coming OS version.
May 12, 1998: Phil Schiller Says OS X for PowerPC Only
The Programming World Needs a New Language