I certainly wouldn’t mind a larger Bitcoin application if it meant we could send an encrypted message along with each transaction. Right now I require an email message from customers who send me bitcoins. This is not ideal because if another person knew about a transaction that was occurring, they could take credit for the transaction by sending a message before the person who sent the bitcoins. About how many MB do you think it would add? Of course these messages will add to the size of the confirmation blocks being stored, so there should probably be a maximum size. Perhaps 256 characters would be a good maximum since the maximum size of an email address is 254 characters.
It would also be nice if transactions included a return address so that if a product or service being purchased can’t be delivered the seller could more easily and reliably refund the bitcoins.