And there's also the volatility of Bitcoin. Businesses would have to cash out frequently to cover expenses. If Bitcoin drops, it would leave Square liable for the difference.
Discussion
As far as I know some of the current solutions let merchant choose to keep btc or to directly cash out to fiat.
Cashing out to fiat uses e.g. the largest mainly electronic store in the czech republic, so that it is not interesting for me to buy bitcoin to pay in it and let them just exchange it directly to fiat.
I think to have there the option is the right way, I would support the stores which keep the bitcoin.