While I doubt I'd quit my day job for it, over the past couple of years I've been poking at my own database-backed shell history. The key requirements for me were that it be extremely fast and that it support syncing across multiple systems.
The former is easy(ish); the latter is trickier since I didn't want to provide a hosted service but there aren't easily usable APIs like s3 that are "bring your own wallet" that could be used. So I punted and made it directory based and compatible with Dropbox and similar shared storage.
Being able to quickly search history, including tricks like 'show me the last 50 commands I ran in this directory that contained `git`' has been quite useful for my own workflows, and performance is quite fine on my ~400k history across multiple machines starting around 2011. (pxhist is able to import your history file so you can maintain that continuity)