Marketplace Private Plugin

It is possible to host a Plugin (and possibly other assets) on the Marketplace privately so that only people you invite can have access to them.

Update - The reason I was curious about this ability is that I wanted a centralized location for pushing updates so the projects could automatically update the plugin.

never heard of that. would suggest you to use your own SCM where you push your plugins, and pull them into your projects (eg as submodules in git)