The history of currency system have been changed several times and now we are used to use cash. So in future gradually it will change and will be invented a new currency system and it's pretty much sure. And many people now don't like to carry cash even it's more insecure. So in near future The popularity of Cash will gradually be decreased.

Bitcoin can be a perfect alternative of Cash as it's much secure, Decentralized and easy to make transections and anonymous. But some limitations are the main problem for mass adoption of Bitcoin. But Bitcoin has some limitations like it isn't suitable for kids and old people and it can't be used without internet.
 So it will be a perfect alternative of Cash in many terms but cannot fulfill every requirements because of it's limitations.