With the new editor widgets added recently a new universe has been open for the devs. But there are some things missing now. In UMG there are exposed widgets that allow us to enter variables such a Strings(Editable text) and Floats (SpinBox), but that is all. And is fine for in game widgets, but the edtior widget require more than that. You can make editor widgets to set variables like Tags, Objects references and much much more. Widgets like that are used in the editor a lot, when making for example variables exposed and editables. I would love to see more widgets for this kind of things exposed to UMG.
TLDR: More widgets exposed to UMG, like the ones for setting Tags and all kind of variables, thinking on their potential use in Editor Widgets.