Your second point is a great point, and I believe that there should be a user prompt every time something tries to read from the password database over any API.

With that said, what's the threat model for the first point? Is localhost interception a serious risk?

As far as I know, localhost can't be intercepted. Except for unintentional mistakes such as binding to 0.0.0.0 instead of 127.0.0.1. And inevitably there are going to be some tinkerers who'll run it over the network because it suits them.

keepassxc-browser uses libsodium's box method for encrypting the messages. Only public keys are transferred between the extension and KeePassXC. You still need a valid private keys and a nonce for decrypting and encrypting the replies. You can read a more detailed description from the github page.

I have been keeping eye on the vulnerabilities and going to be very careful when it is time for a final release. Currently if there's any vulnerabilities, these are almost identical to chromeIPass' possible vulnerabilities.

Well, yes, that's the goal. But it's surprisingly easy to mess up. I think the people here are cautioning you not to get overconfident, and to make sure you research the details of the flaws in other systems.

It is easy to mess up, yes. I'm not overconfident, but almost the opposite. Without being totally paranoid, I'm usually pretty certain something important is forgotten. All help is welcome :)

chromeIPass' possible vulnerabilities being?

KeePassXC restricts chromeIPass to localhost, so data should be safe. Still, chromeIPass exchanges encryption keys in base64. Basically that's plain text. These are the only keys used, so technically it's possible to steal those keys (if not localhost). But if someone has permission to read your loopback or local packet traffic, your info is gone..

Other than that, chromeIPass uses quite old libraries and depricated API functions. Those haven't been updated in ages. keepassxc-browser should fix all issues mentioned above :)

Also, any autofilling is disabled by default.