I filed a bug in the new system for this, since I just encountered the following behaviour in Unreal 4.22.3 under MacOS 10.14.6:
Text Box and Editable Text yields two different types of classes, but Text Box (Multi-Line) and Editable Text (Multi-Line) yields the same editable class.
I hope that this is a MacOS specific bug and that there really exists a multi line text box that can’t be edited in 2019 for Unreal.