In this instance if we are going to generate config I would maybe implement something in lines on simple UI and config api validator ? Then anyone could extend UI and program against backend validator before it would be committed

As an engineer working using vyos and HAproxy in many customer environments I would say to keep those solutions apart. Vyos is a great network appliance and HAproxy is an load balancer. They can work together really nice and I dont see a reason to tie them up together.