Yes it is sound money as every secure token thats good to measure a value with. That doesnt mean that bitcoin is a replacement of any other type of money. Usualy its the bad money that is so numerous and so widespread that it literaly wash out the market of other currencies, like fiat does.
Besides that Bitcoin is way to slow as an replacement for money.
bitcoin is being use as a cash money in the case if someone exchange their bitcoin to the fiat money but I think bitcoin has the ability of buying objects and saving money and to buy anything you want through online payment so I think bitcoin has provide an ease for those who cannot go to the markets and cannot spare time for markets so they love to use bitcoin online payment service.