The question was asked over 2 years ago and clearly it was not smart to try it mainly due to the USB bottleneck of the card reader.
Can we expect the situation to be any different today?
- SD cards are faster (or it's cheaper to get faster ones),
- card readers may transition to USB 3.0 (not too soon?),
- it is possible to just install the system to a SD/MMC (/home on HDD) and use F2fs (with minor tweaking, /boot on a different partition fs, Saucy coming with gparted 0.16). [well I hope the result is better than a live-usb...]
Bonus question: could MMC be better than SD (my Vaio has a dedicated MMC reader that would thus be put to good use)))?