It should be possible, but we already have complete solutions like WordPress, Joomla, PhpBB… for this advanced kind of things, so it would be a waste of time creating just the same in Elixir, if you need a personal customized solution for you, I’d recommend embedding the plugins inside the whole app.
It’s such a pain creating a general CMS solution, as you need to think in terms of reusability, modularity and extensibility among other things. The more use-cases you want to cover, the more complex it becomes.
We’re discussing pretty much the same here: Web Forum Software in Elixir / Phoenix