BTC is a speculative currency whose success caused many clones called altcoins. However, STEEM is technically not an altcoin because it has more use cases than just value speculation like bitcoin. In fact, all second generation crypto tech should not be considered "altcoin" because they propose more use cases for the underlying crypto tech as a whole.
Such lazy application of proper definition is hurting potential adopters who insist that all next gen crypto is simply a bitcoin alternative, or "altcoins" fighting for a piece of the potential currency market which BTC competes in. But when you finally realize that the market which bitcoin is competing in, is limited to currency, you will see that second generation crypto projects are competing not only for a slice of the currency market, but for many pie slices from many markets which are currently anticipating disintermediation. This is where the BitShares crypto-equity brand of thinking about crypto-communities as value generation machines rather than tokens with no other use case besides speculation is ripe to finally go viral. Thanks to STEEM of course.
And if you think that bitcoin has many use cases besides value transfer/speculation, thanks to third party apps, then you have not met Graphene. Functionally, there is no real competition. The only way for bitcoin to compete in new markets now is to fork new code, and since the bitcoin community is leaning toward "less forks" to preserve their advantage of maximum immutability, they will be shut out of new markets before they even begin competing.
In other words, I don't think that STEEM will ever have to worry about competition in the blogging world from the bitcoin community. Since bitcoin does not want to compete with STEEM, then how can STEEM be a bitcoin alternative (aka altcoin)?