In terms of sharing customizations, I think that something like Stylus user themes is a better point of comparison than "full" extensions that alter the core functionality of a product like VS Code.
There's already a UI to create these customizations on individual accounts, so it's just a matter of deciding the best way to aggregate and surface them to everyone.
Looking at User Styles, they have a main landing page that can be sorted in all the expected ways. Clicking into a specific style (this is one that I made), you can see all the metadata, statistics, and code. As the author of this style, I can edit and delete it. Other users can rate the style from 1 to 5 and leave a comment.