Quantum Computers are advancing much faster in calc and storage capacity. In 4 years from now, QCs will have cracked the blockchain, and Bitcoin will be gone, or at least, residing on a QC.

Its true that quantum computers are advancing fast but as far as i know until 2020 bitcoin is quantum computers resistant
They won't tell you when it's working.
but let us be realistic here. if you QC can crack the blockchain, then it can also crack other places with much more money involved. and if you want money you do not go for bitcoin, since an attack for a big sum will be noticed and bitcoin will probably become worthless. so the only reason to do this would be to destroy bitcoin.