The next planned hard fork on the Ethereum blockchain has an official date- October 17th. Until then, the blockchain will run the Byzantium update on the Ropsten test net, where transactions can be tested without a gas price. Byzantium is the first part of the Metropolis stage on the Ethereum project. The updates were split, and the next hard fork, Constantinople, was delayed to achieve a smoother running of the blockchain.
The Byzantium version has been running on Ropsten since September 18.
The most prominent feature of the update would be the possibility for anonymous transactions based on the algorithm of ZCash.
After October 17, users of MyEtherWallet will be safe with an automatic update. Users of Geth or Parity would have to update. There will be only one Ethereum network after the hard fork- it is a planned update, and not a split off where two chains are supported.
The Byzantium update will benefit miners, at least for the next 18 months. There was a visible uptick in mining difficulty for Ethereum starting from September 21.
The update will delay the difficulty time bomb and prevent those difficulty spikes. The change is based on the EIP-649, which is only a part of the changes related to the hard fork. The lower difficulty will also come with a block reward of 3ETH instead of 5ETH, as it is now. Other mining changes include a more equitable reward when two miners discover a block at the same time. The so-called "uncle" blocks also receive a reward, but do not continue to exist as a separate blockchain- only one valid block remains.
Also, new blocks would be discovered about 10 seconds faster. Faster mining will also affect the total supply of Ethereum, which will increase faster. Currently, there are 94.8 million ETH in circulation and in about a year, the supply may increase to above 100 million. Initially, the supply of ETH was capped at 100 million, but with the delay of proof-of-stake securing, the final number may be around 104 million ETH, due to the mining grace period.
For miners, there will be more than a year of hassle-free mining before difficulty starts climbing again. Even a year is a very long time by cryptocurrency standards, but Ethereum has already set the pace to evolve into a very different product.
Despite the successful tests, the Ethereum market price faces very different pressures. ETH still struggles below the $300 levels, depressed by news of further blockages to ICOs across the globe. Ethereum demand has increased because of ICOs, since for most of them this is the currency of choice for raising funds.