Web technology is mature, fully featured, well-understood etc, Industrial controls systems 'suck' by comparison
A 'universal' opcua to restful http bridge is a very nice step to improving the interopability of industrial control systems (not just on the rendering side of things, but with other systems)
Python has been chosen because it is a very popular language with a very 'healthy ecosystem' in regards to available libraries operating systems, users and support.
While python is not the most performant language out there, it's possible to develop a viable product quickly. Since hardware these days is cheap (especially in a controls systems context) the bridge will be designed with the intention that it be run behind a load-balancing proxy server, such as nginx or haproxy
Operating system agnosticism is important to me, i'd like to see more linux machines in a controls systems environment (since it's generally more secure, requires fewer resources, more reliable, etc