This is possible with GAE, which can now load images, etc. Sadly, there is pretty much no documentation except the example of the default widgets cfg and the source code, but it certainly does have very good potential. I'll be blunt and say MG should NOT implement this because that would just slow down the merge, which I say is top priority behind bug reports.
Thinking about it though, not sure how a raster graphic would do for a background image like that when people can use so many different screen resolutions... Would there be a way to resize for every screen size?