One thing's for sure, they can't put much more into an MPC than the 4000 without having some ergonomic and UI genius working with them.
I had a discussion about this recently, basically my arguments are below:
Hardware is less likely to become obsolete than software. Software products are always updating, changing, computers themselves are also changing, getting rid of certain ports and moving to new protocols, how long will USB be around? Will companies port their drivers to the new OS's for recently discontinued products? Or will they let out the new batch of hardware controllers and leave the old ones in the dust? That's obsolete. Ideally you are right, but the reality is that it puts the musician in a state of constant change, requiring costly soft and hardware updates, and prevents the level of mastery that traditional instruments require and is also possible with hardware.
Software that came out in 98 cannot run on the new OSs, and just try to sell it to anyone to reinvest that money into new equipment. Computers are much more disposable, planned obsolescence is really the name of the game with computers. Control surfaces might improve the computer as instrument aspect, but even they suffer from being absolutely useless in the not so distant future, all it takes is a driver to not be updated for a new OS.
On the other hand, look at old hardware, still in wide use, by pro's and amateurs, as long as it makes noise it is not obsolete,
