What problem does this address?

In DataForm there are a variety of controls, e.g. text, textarea, etc, for handling text content, but there isn't one yet for rich text. However for some use cases, such as media (#72612), or editable fields in the inspector sidebar (#71730), a rich text field would come in handy.

What is your proposed solution?

Create a dedicated rich text field control in DataForm that can be used via the string richtext and can also be configured to show the inline toolbar, or to have the toolbar hidden. A visual example of how this might look for a field is: