This is a puppy that will grow up to bite you. It is cute and appealing though.

Your solution implies that all scalars will be scalar coderefs, at least for some set of keys. And Then this set of
keys, or its universal nature, must be unmistakeable otherwise your attempted idiomatic meaning becomes lost
because it is just normal code.

If parameters may be needed you will need to deal with array references or such anyway.

A good programmers' idiom is complete in itself, like an idiomatic phrase in natural language.
Your meaning exists in one place, but must be interpreted in another. This plays against its utility.
I would be more explicit: 

   $foo => \&immediate,
   $bar => sub { "immediate" },
   $bey => [ \&immediate, $arg, ],

   $mah => [ -defer, \&delayed, ],

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In reply to Re: callback or call now? by rir
in thread callback or call now? by John M. Dlugosz

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