Currently if the main root page / is missing the default "Welcome to Platform OS" page comes up, which is totally fine for new instances. It would be great to use the custom 404 page set over this or even be able to customize this page?
Custom 404 page to work for main index page
I think creation of app/views/pages/index.html.liquid is the customization you think of.
You can put a homepage in there (most cases) but just as well you can inform user about work in progress.
In my case the customer deleted their root page by mistake... I would have thought the custom 404 page would have been displayed. I'll make sure we have two 404 pages from now, one for the main page and one for everything else.