There is a downside to the demise of the SD slot: the EOS-1D X will not take an Eye-Fi wireless/memory SDHC combo card.
they suck anyway.. no pro i know would use them.
i returned mine after 4 days.
for studio work you have ethernet with the 1D X and there sure will be better solutions then the eye-fi cards.
Sorry to hear you couldn't get EyeFi working for you. It's not an uncommon story.
Yet there are plenty of professional photographers out there working smoothly with EyeFi. It is necessary to be aware of its limitations. I only use it to stream small jpegs to an iPad with the app Shuttersnitch which is handy for a client to watch the images roll in rather than peering over your shoulder. Attempting to stream RAW files with EyeFi is an exercise in futility.
Still, EyeFi does definately feel like a temporary technology. I feel pretty certain that built in WiFi will be a feature of many new cameras in the not too distant future.