The current implementation of using macros in filters isn't good enough:

<$list filter="[<mymacro param:'value'>]">
...
</$list>

It isn't able to use variables or textreference as a parameter of the macro. I think we had better introduce a macro operator so that variables and textreference can be used as parameter (like the function operator). For example

<$list filter="[macro[mymacro],[value]]">
...
</$list>

<$let template="DDth MMM YYYY">
<!-- variables and textreference are allowed -->
{{{ [macro[now],<template>] }}}
{{{ [macro[now],{$:/config/NewJournal/Title}] }}}
</$let>