The Collapsible composite field could be very useful in other areas of the software. I would be helpful if we could move the field to ui-framework. Currently it resides in the Content Editor module and this creates a couple issues:

1. You need a pro license to use that module
2. You have to install that module to use that field even if you do not intend to use the other features of the module.

https://documentation.magnolia-cms.com/display/DOCS57/Collapsible+composite+field