The problem isn't that it couldn't be done, the problem is that there is absolutely no commercial incentive for anybody to develop one. Epson put their hand in the fire first and got burned. Leica went second and got singed. Who else would want to risk getting a bad rep for quality in return for, at best, a slice of a very small sales "pie"?
I think that if we do see another DRF, it will come from a maker nobody has expected: maybe a Chinese technology company that wants to earn a reputation, or a lens company that could benefit from another platform for which to sell its products.
In another thread somebody brought up Sigma, and I thought that was an interesting suggestion: they make cameras as well as lenses, they've got a lot of development capability, and they're something of a maverick that isn't afraid to go where others aren't (witness their development of their own lens mount for their SLRs, and their advocacy of the Foveon chip.)
If someone such as Sigma came in, though, I predict they'd want to develop their own fully-electronic RF lens mount so they could monopolize lens sales and optimize the lenses for digital imaging, rather than sticking with the traditional but problematic-for-digital M mount.