A Minecraft bug exists since 1.13.2 with /data modify

This bug fix/allow a lot of new things, this bug is really important for datapack 1.14.
this bug will become a new feature (Annonced by "Boq" Minecraft developer).

Doing "/data modify on SelectedItem or Inventory" changes the property of the item.

But this bug has been fixed on Spigot.

Datapack is 80% of Minecraft now nobody use uses plugin.
WIth this bug look the possibilites :

Add/Remove NBT, Change the CustomModelData, Name
Transfer NBT, Store NBT.
https://streamable.com/l51sh
https://streamable.com/moscj

How work this bug in vanilla :
/give @s diamond_sword{a:1}
if item in has a nbt tag the player can modify the item with /data modify.

-this bug has been fixed on Spigot (It work in Vanillla).
-can you recover this bug?