[marc]

Our teams sometimes brainstorm like this, and even if the plans aren't precise, it can be a handy reminder -- just like an underlay for graphic/web design.

Both of these are good reasons, and you could add simple ergonomics, like changing the background colour/image for viewing comfort and contrast with Gantt bar colours.

You might even put project info on a background image, logos, code names etc. to further distinguish projects... there's quite a bit of 'lightweight' utility in there, if you think about it.

...this would be a fairly unique feature, and it just feels like an Omni-kinda thing to to. :)