In doing some site optimization work for a client, I ran into a plugin that does replaces WP's built-in featured image functionality with a separate meta box allowing you to specify an image URL rather than importing the image into your own Media Library.
Recent updates to this plugin broke my client's site, where the posts that had external featured images would not display them. And examining the plugin code itself (poor documentation, direct SQL queries on the database) lends me to believe he doesn't quite know what he's doing.
For my client, I whipped together a custom plugin to loop through posts with that plugin's meta keys, import the image into the media library, and attach it to the post. Finally, it deletes the other plugin's meta key.
Now I have no qualms running the fix on my client's site, but I'm thinking of putting the plugin on the Wordpress Plugins Directory as well. And maybe even a "premium" version with monetization.
I scanned through the WP plugins code of conduct, but didn't see anything listed about modifying another plugin's meta entries. Is there anything unethical about this?