Think of .$identifier as if it was $null($identifier).

A (working) script like this,
Code:
alias test {
  $null($input(hey))
  $null($regsub(1st round) $regsub(2nd round))
}

according to the suggestion could be changed to,
Code:
alias test {
  .$input(hey)
  .$regsub(1st round) .$regsub(2nd round)
}

...not a great implementation, but wouldn't hurt if added. Also, it doesn't conflict with the way mirc works, ie. $identifier in a new line would still be treated as a command as long as it isn't prefixed by a dot.