Thank you, @jacobtylerwalls, for starting this thread. I agree with the sentiment. Personally, I find assertIs less elegant, likely due to my longstanding use of assertTrue/assertFalse.
That said, the code review process must also be considered. Any construct/rule open to interpretation creates extra work for reviewers and may lead to debates over what qualifies as “a boolean produced by Django.” Also, an “if this then that” rule increases the cognitive load for new contributors (or even for those returning after a long absence).
In many cases, assertIs has successfully caught truthy values returned due to subtle bugs and misunderstandings of the expected type.
For these reasons, I prefer that we stick with the current rule. Although somewhat rigid, it is unambiguous, eases the review process, and has proven robust, and could even be automated via a lint check.