Supposedely the project is about just building the platform/infrastructure (which is what the index is) upon which search engines can be built.

These search engines will then have the freedom to define their own search product experience, business model, even ranking of results.

So something even more vaguely defined and detached from real use cases than last time? Great.

It is very precisely defined, you not understanding what they are building does not mean it is not worth the effort.

The above actually defines the scope very well. There is lot more to be built upon it, but it is not what the project is trying to solve.