Writing a fully-fledged RFC1459 parser that handles all potential corner-cases in a secure and efficient manner is actually very difficult. By moving the essence of the protocol to an encapsulation that is based on JSON, it can be parsed with already proven JSON libraries.
As an example, the bug which crashed EFnet at the end of 2012 was caused by an unanticipated side-effect in the way RFC1459 messages are formed. Ratbox is a server which has benefited from the work of many experts on parsing RFC1459, and yet the bug was still there.
A simple JSON representation maintains the serviceability of using telnet as a client, but the proposals made on the bug were ridiculous. Either way, you guys trashed it so it gets buried for now.
It's not about parsing text. It's about enabling extension development outside the limitations of the current message format. IRC today is a collection of contradictory conventions, poorly documented mini-protocols, and messy hacks. A lot of users think IRC is simple because all they've ever done is parsed channel messages. Try implementing a complete daemon or client.