Those will not add an MQTT layer to ZHA, just WebSocket server and client for tunnelling over TCP/IP.
Breaking out some pars of ZHA and moving to WebSocket server and client would not only allow it to be updated separately from Home Assistant’s core but also allow running ZHA on a separate computer.
This client-server model concept is also known as a “distributed computing” or “distributed system”:
" Distributed computing is a field of computer science that studies distributed systems. A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. The components interact with one another in order to achieve a common goal. Three significant characteristics of distributed systems are: concurrency of components, lack of a global clock, and independent failure of components. It deals with a central challenge that, when components of a system fails, it doesn’t imply the entire system fails. Examples of distributed systems vary from SOA-based systems (service-oriented architecture) to massively multiplayer online games to peer-to-peer applications."
“In software engineering, service-oriented architecture (SOA) is an architectural style that supports service orientation. By consequence, it is as well applied in the field of software design where services are provided to the other components by application components, through a communication protocol over a network. A service is a discrete unit of functionality that can be accessed remotely and acted upon and updated independently, such as retrieving a credit card statement online. SOA is also intended to be independent of vendors, products and technologies.”
PS: Such models could in theory also allow other third-party apps to use/control ZHA WebSocket server, as similarly, Z-Wave JS WebSocket server allows many different UI clients to connect / control it.