Sidechains should be used for things that are ok to be a little bit less secure. This can be game data or any social content - but the tokens should be on the highest security level - I would thus leave them on layer 1.
As a side note, the ability to feely generate smart contracts on a side chain would be awesome - to my knowledge this is not possible on hive engine and is also not planned, which I think is not ideal for the system.