There are multiple apps that have added to the protocol. None have failed or caused frustration afaik.
To the memo protocol ? You are the only one developing it so you are the only one modifying the protocol. I don't think there is an alternative serious site that is a "memo clone"
The memo protocol is just OP_RETURN with prefixes. Just because they don't have large amounts of traffic doesn't mean they weren't able to add new prefixes.
