Methodologies are like religion
But this isn't a "methodology" at all. It's a statement of goals.
This isn't an "alternative to Agile", because it isn't a methodology. You can use Agile to achieve this "reactive system".
Frankly, it looks like a bunch of BS buzzwords to me. I write software to meet my customer's needs. "Reactive" attempts to define those needs... but NO, that's what the customer does.
This might be something good to show a client who wants a web site built, which you then proceed to build using Agile or some other methodology. But it isn't a methodology itself, and calling that thing a "Manifesto" is a joke.
"We want a machine that makes things cold. We don't care how it's built. We'll call this... The Refrigerator Manifesto".
Give me a frigging break. In fact I have to think this is actually somebody's idea of a joke.