Support for a second hard drive would definately be interesting to see. I'm keeping my dvd drive external since I never use it, and if I could use both at the same time it would be great. I guess I would still need to switch a hard drive off when I need to use the dvd drive, but it's worth it since that's so rare.
The reason two hard drives would be nice is that you can get a 2:1 gig:dollar ratio at around 120gigs (wait for sales, they do come this low), and I would much rather do that (240 gigs for $120) than pay around $300 for a single 250gig drive.