Please add the ability to insert the previous / next paragraph into the caption when clicking the image widget.
Thanks.
This behaviour (what's allowed inside image captions) is controlled by the schema. After changing these lines:
https://github.com/ckeditor/ckeditor5-image/blob/master/src/imagecaption/imagecaptionediting.js#L49-L53
to:
schema.register( 'caption', {
allowIn: 'image',
allowContentOf: '$root',
isLimit: true
} );
I've got it working easily:

However, it's not possible at this moment to easily reconfigure the schema. Currently, you'd need to patch the code of the image caption plugin. But we'll improve this situation over time.
I'll close this ticket as it DUPs https://github.com/ckeditor/ckeditor5-engine/issues/1367 and because I kinda answered it.
Still, if something isn't clear, let us know.