It's not possible to replace the RSS parser (MagpieRSS) via a plugin

[johnbillion]

r5845 doesn't do as intended.

The file wp-includes/rss.php is loaded before plugins are loaded, therefore a plugin isn't able to replace the fetch_rss() function (which was the intention of r5845) as it's already been declared in wp-includes/rss.php.

Not sure what to do about this one aside from moving fetch_rss() into wp-includes/pluggable.php.

On the flip side, I'm using a homemade plugin to replace magpie using the load_feed_engine hook perfectly fine...

Closing as invalid because you can in fact declare the functions in wp-includes/rss.php with a plugin by using the load_feed_engine hook. I was staring right at it but wasn't using it.

Thanks technosailor!