I think I need to write a bit about the distinction between Flarum's core and its default extensions. This could probably be added to the FAQ at some stage too.
If you set up Flarum core with no extensions, you have will a bare-bones forum with very little functionality. Discussions, posts, users, groups, search, notifications – that's pretty much it. No sticky, no lock, no subscriptions, no tags, no likes, not even Markdown/BBCode... they're all extensions.
When we consider what to add to core, popularity doesn't really come in to it at all. Core is about providing a solid foundation on which extensions can build, rather than a default set of features.
On top of that we have an array of default extensions that we'll commit to maintain and package with Flarum's default installation. This is where the common features like Sticky and Tags and Likes come in.
So when we say something will be an extension, this doesn't necessarily mean it won't be developed/maintained by us or included by default. It just technically won't be a part of the core.
Berlyn Depending on how extension management gets implemented, it might be something as awesome as cloud provided for extensions. You just install the software, go to the admin panel, search for the extension you want and press install. The cloud provider and Flarum could do the rest of the work and bam, you have the extension.
That's more-or-less the long-term goal.
