Have you tried cloudsearch.google.com. It's only available for work accounts. I believe the way it works is, if a document is configured as "searchable" in its permissions or if you opened a document even once, it will show up in Cloudsearch afterward. Assuming access permissions remain.

Oh absolutely, anybody who implements a nice wrapper on google drive with FTS and tagging and hierarchical ordering will be something I will strongly support my org to buy

Looked to see if something like this exists?

I looked but probably not hard enough.