Apart from the problem of the shared state that makes programming difficult, each " knowledge" field needs to have its own data structures and its own rendering mechanisms.
Instead of a single specification that becomes monstrously big that is controlled by some companies that have the capital to engage in its création, the same companies being the only ones to develop the browsers, we would have a multitude of specifications , all working together.
In essence we are again talking about extensibility and lithification. Abstraction plays a vital role in having variation.
https://forum.malleable.systems/t/lithification
That is the way is see Alan Kay’s argument. From a theoretical point , I agree with him. Maybe there are some intricacies that I have overlooked though.