There's a good reason most professional edit suites are built around RAID arrays spinning at 10K...
Yup, and you generally want 256K stripes. The various RAID levels are very interesting depending on what you want to do. Some people think RAID 1 is slow, RAID 0 is fast... But for random reads, RAID 1 slays over RAID 0. The more disks the faster you can read too. RAID 5 has the same read speed as 0, but half the write speed because a write is actually two writes in all cases.
6 10K disks with 256KB stripes would be able to handle 250MB/sec. I'm amazed though at how many people use the default 64KB stripe and don't tune it for what it's being used for. Hey, you're dealing with a bunch of 4MB files on this server, why are your stripes 64KB? Dealing with that now. Some people seem to think RAID is all about storage space/redundancy, but that's not all there is too it as you know!
If that's the rate uncompressed, then compressed it would be (on average) about 40 megabytes per second. That's within the range of current CF technology, even if you're talking about targeting a single card instead of striping it across two.
50% is probably a conservative estimate of the compression ratio. I expect that a properly tailored compression algorithm would get significantly better than that.
Anyway, yeah, you'd need extremely good flash media, but we're talking about an $8000 camera here. Canon would have to make it abundantly clear that the feature won't work with anything less than the best performing stuff you can get right now, but aside from that it shouldn't be an issue at all. The guys that would buy an $8k camera to do RAW video aren't going to think twice about the price of the requisite CF cards, since the total package would be quite a lot less expensive than what they're used to paying right now. They'll be ecstatic that it's possible to get RAW video at all.
Like I said, if Canon can pull this off with the 1Ds4, it will fly off the shelves (at least, compared with what you'd expect from a camera that costs $8k). Nikon would be left behind in the dust, and I'm quite sure that Canon would like that very, very much.
Canon's got a lot of incentive to do this, so I won't be surprised at all to see it happen on the 1Ds4.
I wouldn't give that much credit on image compression, unless you're going lossy. The only time I've seen lossless compression actually shrink stuff down to less than around 70% of size is when compressing text with bzip2. Then again, I don't really deal with image compression too much, so I could be very wrong.