This is a limit in the size of OP_RETURN transaction outputs. Longer messages would require multiple transactions which we haven't added support for yet. Thanks for your question.
Would this require a change in the BCH protocol?
No, just an addition to the memo protocol.
..."carrier transactions"... which is fine and should be able to be implemented I would think... but it would complicate things somewhat (I would imagine).
Polls already use multiple transactions. Wewo and Matter blog protocols use multiple. It's not quite as simple, but it works fine.
As far as I know... transactions with multiple OP_RETURNs in one transaction are considered "non-standard" by miners and are not relayed at present... would thus need to do multiple..
The protocol doesn't prohibit it. A miner could mine a transaction with more than 1 provably unspendable output. The issue is the nodes consider them nonstandard and won't relay them.
