Rockbox ports aren't planned, they're ported by people who own the hardware and have the motivation to look for information on the hardware and the original firmware and are willing to put the work into trying to port it over.
I'm sure this can be explained better by those who have repeated it so many times.
In short, though, unless you and anyone else who wants to see Rockbox on this are willing to spend the time and energy doing the necessary work to make it happen, it won't.
I myself own one, and wouldn't mind seeing Rockbox on it, however as I have very limited codeing experience, no understanding of the hardware and how it works, and no time to apply to learning the code and how the hardware works...