This may be out of scope but would be amazing to figure out. I've seen some odd ball integrations on GitHub that get started then abandoned so they are not contenders.
Just like many places in a hybrid setup with some on prim some hosted services we have a rather large blind spot that currently I can't seem to find a simple way to fix. Hosted side we have OneDrive and Sharepoint being pulled into Enterprise search which is nice but has been limited in success. We still have on prim servers and will for the better part of the next decade. We are not in an industry that can be hosted yes they do exist. With that comes years of PDF's word doc excel power points you name it the common file formats. Is it possible to have Enterprise search index a local file server with millions of files?