Apple does a pretty good job supporting the needs of most people, in a slim clean form factor, with the iMac. It supports memory upgrades, and external monitors. There is a small group that needs nearly every component to be upgradeable or swappable, and they offer the Mac Pro for that use case. I don't see a scenario where the cost/benefit of adding removable graphics cards to an iMac would make sense. I would like to see the hard drive accessible like the memory is.