Not a WIP, been running like this for over a year and have a good user-base. They intentionally kept UI this way so you have access to what course contains but the details are hidden behind the paywall. Videos and content is their USP and they are focussing more on that.
Performance has not been a challenge as video heavy-lifting is offloaded to Vimeo. MOOCs unless of the size of Coursera will never have a concurrency and perf challenge. Are too thinking optimisations too early?
Based on my experience of Wordpress, if you are willing to get hands dirty and look beyond the current theme/plugin bloat, it’s customisable enough to solve your needs. WYSIWYG issues are a result people expecting too much from the themes and in turn themes trying to cater to every possible use-case.
If you are looking for something out of the box, as @dalan said, teachable might be a good start.