We've now added a new feed output option:
Remove images
.
image
To enable this:
  1. Edit your feed
  2. Click the
    Generate RSS/JSON
    tab
  3. Check the
    Remove images as part of cleanup
    checkbox
  4. Make sure
    Clean HTML
    is checked
  5. Click
    Update Feed
    button
Next time your feed updates, images will be removed from the generated feed's item content. You can choose the 'Rebuild feed' action from the feed's actions menu to have the feed rebuilt with the new setting applied (although you might have to wait a minute or two for the generated feed to update).