[Eric V. Smith <eric@trueblade.com>]
Here’s the idea: for f-strings, we add a !d conversion operator, which
is superficially similar to !s, !r, and !a. The meaning of !d is:
produce the text of the expression (not its value!), followed by an
equal sign, followed by the repr of the value of the expression.
... 
The result is a string, so if you really wanted to, you could use a
string formatting spec. So:

print(f'*{value!d:^20}*'

would produce:

*      value=10      *

Although I don’t think that would be very useful in general.

Me neither ;-)  But what if

    {EXPR!d:FMT}

acted like the current

    EXPR={EXPR:FMT}

?  I'd find _that_ useful often.  For example, when displaying floats, where the repe is almost never what I want to see. 

>>> f"math.pi={math.pi:.2f}"
'math.pi=3.14'

I have plenty of code already embedding stuff of the form

    EXPR {EXPR:FMT}

and don't really care whether there's a space or an "=" between the chunks.  "!d" could act like a macro-expansion operator automating a mechanical transformation inside the f-string.  Then I could read "!d" as "duplicate" instead of as "debug" ;-)