Here's a couple of related new ones that fall out of something I'm working on:

• The ability to pass anonymous blocks to subroutines in positions other than the first.

  Ie. Drop the requirement for the sub keyword. Possibly only if the recipient sub is prototyped to take sub references: eg.

  sub someSub (&&&) {
     my @coderefs = @_;
     ...
  }
  [download]

• The ability to pass bare expressions as parameters to user subs.

  In the same way as map & grep can take an expression that is executed repetitively within the context of the function: eg: @array = map sqrt( $_ ), 1 .. 10;

I've no idea if either is actually feasible, but if you don't ask, you'll never know.