I just released a new userscript that allows you to load PlayCanvas Editor plugin scripts directly from your project.
Create and develop plugins right in the Editor!
Check it out: yaustar.github.io/playcanvas-editor-api-tools at master ยท yaustar/yaustar.github.io ยท GitHub
Things to note :
This is a personal R&D project, not an official PlayCanvas feature and subject to a lot of change
We are planning to develop official Editor Plugin support though. The feedback/tests/etc that we get from this will help drive that development