I actually spent years on-and-off building this. What I found is I don’t really care about MOST information I store, and the pieces I DO care about are kept in a place I can easily memorize (eg a couple folders on iCloud).
I ALSO found that nobody really wants to pay for a product like that (in my case, it was a desktop app that’d index everything on your machine - no cloud, etc). Similar products come and go every other month, and they usually die because 1) indexing isn’t cheap and 2) people don’t seem to use said indices much, in practice (crazy high churn).