But it really is nearly abandoned, and outside of the happy-path the primary author uses it for, it's desolate. There is no community around growing its usage, and pull requests have sat around for months before the maintainer replies. Which is fine if that's what the author wants (he's quite busy!), but disappointing to potential adopters. I've looked at using it, but with data types that sit outside the author's use case, and you'd really need to fork it and change code all over the repo to effectively use it. It just never hit the ideal of "store everything" it promises when it has hard-coded data types for indexing and system support.
(and yes, I did look at forking it and creating my own indexer, but some things just aren't meant to be)
I just added support for perkeep in Filestash last week (https://github.com/mickael-kerjean/filestash)