Interesting post! Perhaps next we will see faster LAN speeds. 16GB/sec LAN would not be a bad thing. It would certainly take advantage of faster HDD speeds for file transfers.
Anyways I understand that SATA-Express will max out the bandwidth of your PCI-E lanes, as the bandwidths listed are consistent with the maximum bandwidths of the PCI-E lanes. It seems odd that there isn't any speed lost due to processing on the card, but perhaps I am wrong.
Also what would be the use of these new platforms? I understand the 8GB/sec but not 16 yet, as I have not seen any drives of any type come close to that kind of bandwidth unless you have a striping pattern straight out of Hell itself. The only thing I have seen come anywhere close to the max of current SATA platforms would be my server itself, with 8 drives (at 10K-15K RPM) all in a RAID5 array.
But hey, a faster bus can make anything possible! Why not do something that can be done?