I had plans to start mining Ethereum at the end of 2017 but I then read that Ethereum was going to change to Proof of stake so mining would be useless and I didn't want to invest in graphic cards that I may not need. So, is this still in process or has been canceled?
It is still in the process and i guess you should try to read this one https://github.com/ethereum/EIPs/blob/master/EIPS/eip-1011.mdAnd there will be another announcement regarding it due to the byzantium update and ethereum POS will get another delay (there was no ETA for this maybe soon)
But POS will not be implemented instantly but the block reward will be decreasing a lot from 3 ETH for each block to the 0.6.
