Audience
Web developers
As obvious as it may seem, one of the main users of this CMS would be a web developer. The maintenance, upgrading, and initial set-up of the website would probably be handled by a user that is well-versed in the ways of the web. Through Subrion, a developer can make use of HTML, JavaScript, PHP, and SQL.
For example, a developer might edit some of the site-wide settings using the CMS while also editing the backend files of the site. A developer working with the site's databases might also make use of the site's "Manage Databases" page, where databases can be manipulated directly through the CMS. Certain bits of HTML code can also be changed and added via the "Manage Blocks" page, where a developer could insert a code snippet almost anywhere within the site.
Moderators
Seeing as the site can be used to manage user-created content, it is likely that this content will require moderation. A moderator can screen content before it becomes public on the website, and has the ability to delete members or change their settings.
Site owners with limited/no knowledge of HTML
The CMS can be used, on a smaller scale, to update minor portions of the site without the editor having any understanding of HTML. For example, certain content regions of the site can be updated by entering new text into a text field.
Bloggers
With the correct plugin, a blog can be installed onto the site. A blogger would be able to use the plugin to manage their posts and update their site with new content. They could also choose whether or not to use HTML in their post or not.