Well you can't currently run Rockbox on it at all.
Technically, it should handle a different firmware then the one that is actually installed...
But the firmware has to be specifically created
for that hardware. You can't just take firmware from an iPod and expect it to work if you try to install it on your television. They are different devices with different hardware. If you know what a
driver is on a computer, a very simplified way to put it is that Rockbox doesn't have drivers for your player. Rockbox does not know how to use the screen, buttons, sound hardware, etc. in your player.
But yes, it MAY be possible (I don't know - I don't know anything about this Intenso Video Cruiser) to one day run Rockbox on it, if someone (i.e. you and/or people that you round up on Intenso Video Cruiser forums to help you) actually does the hard work to port it - see the link in my previous post.