For Discourse instances hosted by us (discourse.org, Civilized Discourse Construction Kit Inc), you need to be on our Enterprise plan in order to install custom plugin bundles, because we use multisite for standard/business customers and a plugin installed for one customer in a multisite config runs for everyone, which can cause Confusion and Delay if there’s bugs in the plugin, or incompatibilities with other plugins, or any number of other potential issues.
If you’re an Enterprise plan customer, just drop us a note at team@discourse.org explaining what you want, and we’ll get it sorted for you.
If there’s a plugin that’s high quality and widely sought after, we do add new plugins to our standard/business plans from time to time, after doing a lot of verification to make sure it’s not going to cause problems for customers who don’t want it.