With the new NBTEditor, you are now unable to set the glowing effect on items (where the outline is highlighted) when dropped.

You seem to be able to specify glowing with EntityNBT and PotionNBT, but can't set on items themselves. Could this be re-added with the option to change the glowing color?

The glowing effect is a property of the dropped item entity not the item while its on the players hand. This means you cannot set it with the /nbti command.
To make a stack of glowing items you need to create a BoSs for items with /bos get minecraft:item then set it glowing with /bos var Glowing true then set the item stack with /bos var Item (drag the item to the slot).
I'm not aware of a way to change the glow color.