State of Plugin System and ability to template sections

Hello there,
I have to Feature Ideas. The first is section Templating, where you can Templatemize Textsnippet and add theme with a command to the Document.
It would also be nice if its recursive (also for document templates) where I can define a Command, which gets executed when inserting it in a document. So if my template(also document template) includes a /stuff as a Placeholder than it gets replaced.

We have currently for other menbers shortnames , like JS for John Smith , it would be nice if I can also type @JS and it links to the Same thing like when I type @John Simth . alternativly a /js which replaces it with @john smith would be okay.

so I found the issue #2219 where a system to add Plugins was discussed, but I also saw that there is a plugin's directory. But nothing more . Is it possible to add these features myself without reading the whole Codebase or is it currently not possible.