Of course, whatever works for a professional, he or she will use it- these rigid boundaries are merely theoretical.CFast is the designated replacement for CF cards. CF cards are based on the PATA bus so are constrained to 167MB/s of UDMA 7 spec. Now CFast on the other hand uses the SATA bus that is currently limited to 600MB/s
I am not very familiar with CFast. They seem to have been around for a while, why hasn't any major manufacturer started using it yet? What about the Nikon XQD cards?- I believe they can write as fast as 500MB/s (the newer version might be even faster)
4K resolution video cameras that currently use CFast are those from ARRI and Black Magic Design. ARRI Amira allows for up to 200fps vs the more standard 24p/30fps/60fps 1080p video we are more familiar with.
It is very much possible that we'll be seeing SLRs with CFast next year or 4 years from today. There is still some wiggle room with CF cards at say 1100x? Speeds of current CF cards top 1066x and are hella expensive.