Is this still going to happen? If so when?
Custom widget have been supported in WAB since the initial Beta release. There is currently no UI for adding custom widgets (that is coming in future releases), but all you have to do is copy the custom widget to your Dev versions widgets folder and then the next new app you build you will see the custom widget in the widgets tab. If you need to add a custom widget to an existing app then you copy the widget to the apps widgets folder and then you have to manually input the widget json into the apps config.json.
I assume you are asking about adding custom widget in the AGOL version of WAB, since this is pretty easily done in the developer version, right?
When was there an update for this in the developer version? What custom widgets have you seen? Please send me the link to this. I don't use the AGOL version.
There is a space just for custom WAB widgets:
Web AppBuilder Custom Widgets
There you will find posts like this: Roberts Custom WAB Widgets
Where I list my current widgets
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