As someone looking to buy the XQD enabled Nikon D500, this issue just hit my RADAR. I think SD is the standard because of low cost, ubiquity and it meets the needs of almost every use. However, there is certainly a small and important market for high speed cards. But can the market support 2 different standards? This could really end in tragedy for some users of one format or the other. I notice the Nikon D5 has a service center replaceable card module (CF and XQD). Wonder if they have a CFast module designed and ready to hedge their bets?
Yes, I think the market can support the two standards, It always has done it. CompactFlash and SD in the past... or if you go even back we had MMC, MemoryStick, CompactFlash, SD some years ago... I think SD will continue to be the dominating one for a while. Maybe we will see a separation between SD for "non-pro" level and XQD and CFast for Pro level.
I highly doubt Nikon will do CFast module in the future... the reasons, my next paragraph...
Oddly, you would think Sony could work this in their favor. I like the XQD card size and it looks like better connector than the fin on CFast, but like Betamax and Memory Stuck, Sony has a nasty history of taking the better technology and arrogantly assuming people will pay extra for it. They just don't understand "good enough" and value.
XQD was designed by ScanDisk, Sony and Nikon together (
https://en.wikipedia.org/wiki/XQD_card ), so Sony bets will be XQD. They are already doing products that use this format: check the specs for example of their FS7 camera:
http://www.bhphotovideo.com/c/product/1082825-REG/sony_pxw_fs7_compact_4k_xdcam_with.html . Maybe in the future they put it in their E mount FF cameras... but I'm happy they are still using SD for the moment... I have tons of SD cards...
CFast is the natural evolution of CompactFlash format. CompactFlash is based in the PATA standard to connect harddrives or CD/DVD-Roms units in PCs. Since many years ago the PC industry moved to SATA, and CFast is based in the SATA standard (Right now the PC industry is moving again to even faster connectors, mainly for the main harddrive, connected directly to an PCI-E bus). For the moment the companies I'm seeing using CFast are Arri, Blackmagic and, of course, Canon (probably I'm missing someone... I'm not following too much the video world and those guys are the ones that benefit the most with this new formats).
For the moment I'm only seeing Lexar and Sony doing XQD cards (curiously ScanDisk, one of the companies that presented the format back in 2010, is not commercially selling XQD cards at this moment... although this will probably change in the future now that more cameras are using it). Prices are high at this moment for XQD, comparing to CFast, but I expect that they will get lower overtime, as usual.