I know this was used before in PlayStation Home, but this time, it involves the XMB and loading/running a few things.
Using a proxy program, you can redirect the images/videos that show under the new "What's New" section. If one of those items is a video, you can launch a video player from that icon. I'm no genius, but would it be possible to trick the PS3 into thinking it's loading an MP4 file when really it's loading something different? Also, the 'videos' that show up in each of the little 3x4 squares are flash videos. I don't know if there is anyway to do a specific command for the PS3 using a simple flash file, but I did try replacing it with a game from miniclip (I could have found something that related (Closer to the same size, a video--not a game...)) and it just showed up blank, leading me to believing that I might have something. So then I replaced it with a very large image in my photo folder on my PC and it was scaled down very well.
Anyway, that's all I have right now...
Similar thing has been done on the VidZone application, the intro to that is just a simple flash file and someone managed to replace it and it showed the new flash intro instead of the default one.