This has been answered several times already.
- those who need more than 16gb ram,
- those who need to use PCI cards (audio, video, SCSI,...),
Both valid! The others, not so sure. I’m also thinking of just getting a new, fast Retina MacBook Pro, hooking it up to my NEC SpectraView’s (no issue with matt/glossy and Retina on location). I don’t see why setting up an external RAID would be an issue, especially in light of the Thuderbolt options.
The Retina is said to be able to drive THREE external displays.