I don't see much of a downside as long as Reddit gives a price quote in bit coins and convert it the main currency Reddit uses, probably USD. The main problem for main-stream business using Bitcoin I think is the volatility. Losing money because the currency fluctuates around 10% every 30 days is horrible.
There are services (e.g. Bitpay) which remove the currency risk for the seller. The seller can set their price in US $ or whatever and receive the payment in that currency while the purchaser has the option to pay in bitcoins at the going rate at the time.
