[Terr_]

In the author's example it's about internal consistency, a bunch of other similar items are already singletons.

Better a consistent-but-suboptimal architecture than a random grab bag of varying quality.

[jemfinch]

A journey of a thousand miles starts with the first step. If you're committed to code quality, existing low quality code should not prevent you from doing the right thing with new code; on the contrary, doing the right thing with new code will free you to refactor or update the old code to be cleaner.

[Terr_]

Again, I refer you back to the original scenario: The inconsistency is presented as accidental or unintentional, not as the first step in a cohesive long-range plan to refactor the codebase.