Is your feature request related to a problem? Please describe.
Item caching is needed for showing a shield when the player is blocking. The shield makes blocking less "laggy"

Is this related specifically to ViaFabric?
(Optional)

• It seems to not apply for ViaVersion/ViaBackwards/ViaRewind installed on Bukkit/BungeeCord/Sponge/Velocity servers.

Describe the solution you'd like
A clear and concise description of what you want to happen.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Which versions is this for?
1.9+ clients on 1.8