Agreed with John that this would be a great plugin.
Zend includes a library for retrieving data from YouTube, which Omeka has in 'libraries/Zend/Gdata'. You could use that to get the data for most anything on YouTube, not just the video itself. I haven't used this yet, but Zend has docs on Using the YouTube API that should be useful.
I could see a plugin that would do the following:
- Create a new item type called "YouTube Video", with a field for the video ID or the video's URL. Or, add a field to the Moving Image item type for the video's URL/ID. Something unique like 'YouTube URL', since 'URL' is already part of other item types.
- Filter the display of that URL or ID field using the Display Item Filter to use a function to embed the video instead of just displaying the URL. Something like:
add_filter(array('Display', 'Item', 'Item Type Metadata', 'YouTube URL'), 'your_video_embed_function'))
We use a similar filter in application/views/scripts/custom.php to filter any untitled items.