Hey there!
I’ m currently working on a custom system for handling widget in a game using UMG.
I chose to stop working on that for a little moment because I’ve seen there would be some work going on with UMG –>Trello, and I would like to not end up with a system being unable to use new features or, in the worst case, being broken by an engine update*.
My system uses a subclass of UGameViewportClient** as a “widget manager” class, and is doing a bit of stuff:
-It keeps track of the widgets being displayed;
-It closes automatically widgets that should not be displayed together;
-Gets notified by other classes when It should display a group of widgets together (example: showing widgets health/stamina/lice count/etc when the playercontroller possesses a character and removing them when the player controller does not possess a character anymore…);
I’ll want to add some stuff for the future too, these are the two most importat things:
-Focus management;
-Keyboard input handling;
(Possibly also dynamic styling (being able to draw on widgets), but that’s totally not critical.)
So my question is: How much stuff is going to change with what is coming? And in how much time is it going to come?
I would be happy if someone who’s working on this would give an answer, because I need to choose whether I should continue working with what’s already here or if it’d be a better option to make some progress on a different thing and come back to this later. 
Thanks in advance for replying, and happy coding! 
*Yeah I know that it is recommended to stick with an engine version for developing. That’s another topic however.
**Yeah I know that it was designed to be used with slate widgets instead. For many reasons however, I think it is the best class to use for that purpose.