The KeePass format has been around for years. I don't really understand why people keep using pass, or why it bills itself as the "standard" Unix password manager.
There are also already command line KeePass utilities, like passhole [0] (mine) and keepassxc-cli.
Any program that is GUI first (like keepass) cannot be the standard UNIX password manager. Furthermore, `pass` fits nicely into the philosophy of small reusable components. It is a small amount of shell scripting wrapped around two other commonly used tools: Git and GPG.
1. Without knowing exactly what counts as an "end-user", 15%. This is low for two reasons, 1) because I can SSH into a plethora of non-graphical systems, which I assume are the majority; and 2) just to be difficult and pedantic with the new Wayland systems for example.
2. Should be like 95% ;)
3. Without ever having used KeePass, I'm quite confident of the answer to this one... 100%. Is it officially supported and easy though?
4. Also 100%! But not happily.
Sorry, without some additional context I can't really give you satisfying answers I fear.
> Any program that is GUI first (like keepass) cannot be the standard UNIX password manager.
Why is that? Unix != lack of UI (NeXT, Solaris, any Unix descendant with a port of CDE), and being GUI first doesn't matter if there is good CLI support.
>why it bills itself as the "standard" Unix password manager
It's a smallish (<1k loc) wrapper script around GPG, a tool basically omnipresent, and passwords are saved in an hierarchy as regular files. Essentially it integrates well in the existent ecosystem and is easy to extend.