I just ran across this plugin, and it looks great! I was wondering about the addition of a feature to support pulling first from a custom field, rather than the featured image. The reason I'm looking for this, is that a lot of modern themes use the featured image as a more full-width header, so they have a very wide aspect ratio.
While this looks nice for the posts, it wrecks havoc on all kinds of feeds that require a more square aspect ratio (or, often unwelcomed cropping). I'm having to look into custom fields to store an image specific to this kind of purpose, so it would be nice to be able to check a box put in a field-name that the plugin would first check.
I know the plugin could be modified, but figure more people might be running into this kind of issue, so it might be a welcome feature. Thanks!