Users need to be able to re-order layers in the WAB LayerList. And perhaps even make their own Groups. At least, as options to enable.
We need Groups for webmaps. Partial checkbox and ability to allow a sublayer to turn on even if Parent(s) are not, at least as a programmer's option.
I'd be happy if Esri incorporated my metadata dialogue boxes.
Allow end users perhaps even to change symbology.
Some of these are good too. Advanced TOC Visual Interface
These are more important than the Cost Widget for example. Users still find the layerlist very difficult. It is harder because I have to make the top level checkboxes on so a sublayer turns on in one click but have to tell users to ignore the fact it's checked because there is no partial checkbox and they should know to always expand the group to find out. Not a good metaphor. Also without groups in webmaps the layerlist gets cluttered fast. Multiple layerlists is a workaround but sometimes not an elegant one.
The layerlist can be both simple and powerful. Discoverable, intuitive, powerful.