Currency volatility was an issue on these other sites as well, although it's somewhat extreme with SIGT at the moment due to its being so new.  I'm sure once the volatility decreases and/or the value steadily increases it won't be so much an issue.  Sites that used BTC had sellers adjust prices manually add they didn't have any automated corrections.

That's definitely an interesting idea though. The market could even provide the seller an option of price corrected listings or "brave the market" listings where one could win or lose depending on how the coin value changes.