Currently the usage chat messages are created as base chat messages with flags.dnd5e.messageType set to usage and other details also stored in flags. The ChatMessage5e class also contains a lot of logic that is specific to just usage messages. Creating a new chat message type for usage would allow the data to move from flags to the system data and would allow some cleaning up of the ChatMessage5e class. It would also open up the possibility of sharing some code with rest & turn messages.