Provide plugin architecture so developers can register bundles for editing/displaying field types.
Provide a plugins folder where developers can drop in a bundle for a component that can edit a field type - editor should support single or list of values. This would allow indy devs to add mapping components for postgis or master detail editors or styled text editors or whatever...
From a technical point of view, I'm not sure how easy this is to pull off, given that Postico is sandboxed. I don't think it's possible to load arbitrary code into a sandboxed app -- that would circumvent the point of code signing etc. So extension would have to be written in a scripting language (maybe Javascript?)
But technical issues aside, this would require a pretty major time investment on my side to provide the APIs, and I'm not sure if people would really start developing extensions. My experience with Sequel Pro suggests that the appeal of writing extensions is limited.
But instead of actually implementing this, I can make a different offer: if you are interested in developing a specific extension or a plugin for Postico, please contact me. If you develop a useful component for editing a field type or similar, I'll try to find a way to integrate it into Postico.
JavaScript plugins/extensions would definitely work. It's just reading a file and passing to a bundled Node.js, no code signing necessary.
I'm interested in developing a WakaTime extension: https://wakatime.com/help/creating-plugin