Let me be perfectly clear on this:
Nobody has done any sufficient research or investigation on the iPod Classics for anyone to tell how feasable a Rockbox port is or not. But, based on the assumption that the firmware and design choices are similar to that of the Nano 2nd generation, it offers great challenges to any hacker wanting to go down this road.
Many many people confuse this matter with the recently discussed Apple adding a new checksum to the itunes database, and then the subsequent “crack” of that system. This will only allow Linux-users to use these ipods. It certainly does not in any way make it easier to run alternative firmwares on them.
I would rather say that you should all take this as an indication that Apple really doesn’t care one bit about Linux users. In fact, they only care for those who buy their whole package and that package is Windows with itunes or MacOS with itunes. If you’re not buying that concept, you should avoid Apple. Yes I really mean that.
To get Rockbox running on these models or any of the other newer ipod versions, we need fearless and skilled people to get players, rip them apart and do some actual hard-core research on how their internals work and how the firmware is stored and how firmware upgrades are made etc. The same old new-rockbox port drill.
There might be “an opening” to this device using the DFU mode.
Update: during July 2009 some people in the #linux4nano-dev channel managed to run code on the nano 2g (thanks to an exploit of an buffer overflow) and since then there have been fierce activity and custom code seem to run on the iPod Classics too. Still a lot of work and problems to overcome for a Rockbox port to become reality.