Like I’ve said elsewhere, the Projucer GUI editor is kept around for legacy reasons and we’re not planning on adding any new features to it.
The world has moved on since the days of these static layout editors and all the smart money is now on things like FlexBox, which can handle complex, dynamic layouts. That’s the direction we’re going in the future, so it’d be unproductive for us to spend time improving this deprecated stuff. (Of course, feel free to send us a pull request if there’s any easy additions you want to make to it which you think would be useful to others too)