New NBT tag idea

I think it would be cool if we could get a nbt tag that can be used on players or something similar. I've seen people ask if its possible to change a player's active hotbar slot. For example: If a player's active hotbar slot is 4, and it needs to be 0, you could use a command block to forcefully set the active slot to 0, like "/data merge @a {ActiveSlot:0}" or something.

Thanks :D