- revisionist history. For most intent and purposes, Perl 5 and Perl 6 are two different languages and pretending otherwise helps nobody. In fact, it just creates misunderstandings and misplaced expectations. But why didn't they change the language's name a lot sooner? I honestly don't know. If many of the people involved in the project would've acted sooner, things such as clarifying that Perl 5 and Perl 6 are actively-developed, independent and different languages, even when the names suggest otherwise, would be things of the past. Nonetheless, even now there's the alias Raku, the name Perl 6 is the most used and probably will be for time to come. Will it catch on?
- scope creeps. As you state, Wall's goal was "to remove historical warts, clean up the language design, etc" which he deemed "the community's rewrite of Perl and of the community." but as we all know, things changed along the way (e.g., untimely delivery) and Perl 6 turned out to be a total different language to Perl 5 or to what many people envisioned as the replacement for Perl 5.
* referring to Perl 6 as Perl, or
* mistaking Perl 6 for Perl 5.
Although from the same family of programming languages, Perl (or Perl 5) and Perl 6 (or Raku[1]) are two completely different languages.
The article is about Perl 6 (or Raku), not Perl 5.
[1] https://docs.perl6.org/language/faq#What's_the_difference_be...?