It’s been done for Sony cameras a while back. One of the tools that lets you get into the camera’s firmware is Sony-PMCA-RE. As far as I know this is not the only one either.
It’s not a powerful as a Magic Lantern, but that’s not the point, which is that camera firmware hacks are still going on.
As long as there is a reason and motivation someone will figure it out.
It’s pretty much the only thing I use. Instagram is terrible, but Flickr has remained pretty damned good.