It's not as critical as you might think. Remember that Steelheads already use a kind of "chopped up" representation on their disk, and are typically not far away from clients and servers. Also, the Steelhead's disk without encryption contains identifiable fragments, but assembling larger documents typically requires knowing the traffic that passes through. So we've always had the nice property that the traffic doesn't make much sense without the appliance, and the appliance doesn't make much sense without the traffic -- which isn't necessarily true for some other ways of speeding up network traffic.
An additional pragmatic issue is that an attacker would generally find it easier to get data of interest from a client or server than a Steelhead.
Another interesting observation is that there are some kinds of data you aren't allowed to put on a disk, even with strong encryption. The 3-digit security codes on credit cards are one example. So for customers with those concerns, it's actually more important to have good flexibility about which traffic goes onto the disk and which is only handled in memory. Fortunately we already had those kinds of capabilities in previous releases.
