Maintenance mode & 404 page

We have lots of modules and those modules need upgrades from time to time. I want my users to see NPM maintenance page instead of an unexpected error page.

So basically what we want is this .

----------------->

or

http://www.smashingmagazine.com/2009/06/12/effective-maintenance-pages-examples-and-best-practices/

https://www.google.com/search?q=maintenance+page+error+page&newwindow=1&espv=210&es_sm=93&source=lnms&tbm=isch&sa=X&e…

We want to be notified when a user come across an error page like "There was an error communicating with Orion server". This is crucial for us. We may never know about this error. Most of the time it is fixed in a short time by itself.

Edit: I would like to improve this idea to a whole new level. Why not NPM handle some of the well known error codes like 404.