What about using the wireless on the 6D to send/backup directly to tablet or PC instead of needing dual slots?
You can also then run cloning software on your laptop or even directly backup to the cloud (like dropbox) on the fly as well.
An excellent idea whose time has come!
Absolutely! I just did that for a kiddie portrait shoot at a local zoo event last week, where I shot about 200 portraits in 2 hours. I configured the 6D to save RAW+JPEG on the SD, and set up the EOS Utility on a laptop to pull just the JPEGS automatically over WiFi to a laptop as I shot (for immediate 4x6 printing and backup), and it worked flawlessly. Pics arrived on the laptop and showed up in Lightroom within a few seconds (using Auto-import), and it never missed a beat.
You do need to watch your batteries when using WiFi, though, because I used up 1/2 of the capacity of an OEM battery within the 2 hour shoot, but I had spares just in case.
Great option to have, particularly if you want to hand out quick prints to participants (I used a Canon Selphy dye-sublimation printer for that purpose). Even better than dual slots for that particular scenario, because you don't have to keep pulling cards to print and worry about keeping track.