There are a lot of hurdles. I'm not exactly sure why an end-user would even want to use ISO20022. Some end-user system may use ISO20022 behind the scenes, but the UI's are very simplified. ISO20022 as far as I have used it (20+ years in finance) is for payment networks. And a random person can't just send messages on any payment networks that I'm aware of. These payment networks generally exist as message queues that are interconnected and they use ISO20022 as the data format.
Not to mention that the flows of ISO20022 messages are full duplex. If you send a message you need to be ready to handle a response (acceptance or rejection of a credit/debit for example).
