I'm not sure I agree with this analysis.

Template.__str__() is equivalent to Template.__repr__(), which is to say that these aren't f-strings in an important sense: you can't get a useful string out of them until you process them in some way.

The expectation is that developers will typically make use of well-established libraries that build on top of t-strings. For instance, developers might grab a package that provides an html() function that accepts Template instances and returns some Element type, which can then be safely converted into a string.

Stepping back, t-strings are a pythonic parallel to JavaScript's tagged template strings. They have many of the same advantages and drawbacks.