Hi Alexei,
You'll need to study the existing code to see how it handles uploads and enforces correct permissions.
If you want to have a plugin for TinyMCE integrated it is up to you to propose how to integrate it and to explain how it benefits users compared to the existing functionality for uploading images, does it work in all browsers and other considerations, etc.
But to be considered for integration in mojoPortal the license of the plugin is also very important, it must be a compatible license, nothing under GPL can be included.
Best,
Joe