A feature that I would like to see is a hover button property in the Boxes (from the Gui). This property would allow you to create an event whenever your mouse hovers over the button. (Without coding) In this, you could choose to change the size, position, texture, and run a script. Running a script would be the thing people would probably mostly use.
Since the Defold have only low level api for your GUI interface, you can use Druid GUI Library
Druid have hover component: https://github.com/Insality/druid/blob/master/docs_md/01-components.md#hover