All of that information is discussed in recent @steemitblog posts. The short version is that the Steem blockchain is hardforking, but thanks to Steem's governance mechanism, when Steem hardforks it is more like an "upgrade" and so no "sister-chains" like BTC or BCH are created. Steem moves to a new fork and the old fork is abandoned. Cryptocurrencies themselves do not fork, only blockchains fork. New "sister-currencies" are only created when a blockchain forks, but the old fork of the chain continues. So BTC exists because someone created a new fork of Bitcoin while the old fork also continued to run. Since there were 2 blockchains they needed two different cryptocurrencies. Since only one fork of Steem will continue after the hardfork, the currency of that blockchain will remain STEEM. This hardfork contains no changes to the STEEM currency.