I think I misread your comment - I had interpreted it as suggesting that exchanges should be required to issue IOUs for new forked assets, which has serious practical issues.

Of course, saying that coinbase balances are IOUs for bitcoins is basically what happened here, and apparently people aren't happy about it. While you could change the marketing material, I don't think it would do much to change the outrage in this case; I very much doubt people will pay attention to such a nuance when they apparently couldn't be bothered to temporarily withdraw their coins.