I’m preparing to use the Maintenance mode.
In my opinion the default maintenance page is nice, but unusable due to it’s huge size (220KB) and lack of CORS support.
We have a project that serves API responses in JSON format. Switching it to maintenance mode would mean that each request will download 220KB response body just to read it’s status code or fail due to missing CORS headers.
Luckily, the option to provide custom maintenance page solves all these problems, but I think that this is an issue which could be solved at the Render side for all users.