Blockchain isn’t currency. Blockchain is a digital ledger. It’s a way to keep track of ownership of anything. You can use blockchain for houses, you can use it for digital goods (like videos or Bitcoin).
Bitcoin and Ethereum are currency, just like dollars or Euros, and can be traded. I think that eventually you’ll start to see businesses accepting them as currency, but that’s going to take time.
About the taxable part, I think that’s up in the air right now.