I don't think nested modifiers are a good idea. The result would be too complex and hard to read. If you need two "levels", change the outer one to an ordinary loop or conditional statement.
I don't do thinks like this, but it might be handy. It wil make parsing harder again though so I doubt it will be implemented.
Snippets of code should be wrapped in
<code> tags not<pre> tags. In fact, <pre>
tags should generally be avoided. If they must
be used, extreme care should be
taken to ensure that their contents do not
have long lines (<70 chars), in order to prevent
horizontal scrolling (and possible janitor
intervention).