[nemetroid]

The wording on this page suggests that it is a policy:

https://wiki.archlinux.org/index.php/DeveloperWiki:Patching

As you say, the page notes that "[the] policy is intended to suggest, not to enforce", but having a policy is orthogonal to enforcing it.

[Foxboron]

And as a packager for Arch the past 3 years: I had no clue this page existed. Evidently we are bad at these policy things. But I'd rather call them social norms then packaging policies.