It would be good if we had something that was neither excessive verbose
nor painfully terse, required nothing but ASCII, that was similar enough
to dict unpacking to suggest a connection, but without being confusable
to anything else even to newbies, was self-descriptive without needing
much or any explanation, cured Covid-19, brought peace to the Middle
East, ended poverty, and improved the level of political discourse on
social media.

But I fear we may have to relax the requirements somewhat :-)

My requirements for this syntax are:

...

- it ought to be something "like" an expression, rather than a mode
  that has to be turned on and then applies to the end of the function
  call; 

- if it actually is an expression, that's a nice bonus, but it's
  not essential;