With memory cards supporting UHS Speed Class 3 (= minimum 30MB/s) selling for under U.S.$100, and the smaller form factor, I don't see any reason to keep supporting CF any more.
Considering that my old 7D hit write speeds of >45 MB/s, I don't see a card which would take 50% longer to clear the buffer as a viable option. Also, highest SD card speeds are only achieved after a low-level format, so if you don't perform that time-consuming in-camera task frequently, your speeds get even slower.
Time consuming? Takes no more time at all to initiate the function, and the actual format only takes a few seconds, of which you are not obligated to watch it carry out. Hardly a valid argument. The write speed issue is clearly a problem. Until the write speeds are improved the buffer fills much to quickly when shooting to SD.
A in-computer low level format writes 0's or 1's to every memory cell, and takes a very long time. The in-camera low level format is apparently much smarter, because it seems to only take seconds. I think that its finding just the cells that are not zeroed and writing them, while a in computer format is testing every cell to verify that it works. That's what you should do to find card issues, but the in-camera low level format will recover the lost speed.