[nl]

Are you conflating "single server" and "desktop computer" here? It sounds a lot like you might be?

Because almost everyone already uses the model of co-locating the search index and query code on a single computer (both Wikipedia and Stackoverflow use Elastic Search which does this).

They use multiple physical servers because of the number of simultaneous requests they serve.

This has never been the use-case for Hadoop.

I've built Hadoop based infrastructure for redundantly storing multiple PB of unstructured data with Spark on top for analysis. This is completely different to search.

That's very different to the Wall St analyst running desktop analysis in Matlab, or the oil/gas exploration team doing the same thing.