I’ve seen articles lately that many large banks including, HSBC, Deutsche Bank, Citigroup, and Bank of America are exploring the use of Blockchain. Knowing these banks, they would surely love to use their own currency instead of bitcoin. Given this, could Blockchain used for a different currency, leaving bitcoin behind?
The general idea here is that the blockchain provides some (really cool) new building blocks for us to play with:
Once something is accepted into the chain and has N confirmations (typically 3+, sometimes 6+), it's extraordinarily unlikely to be deemed invalid.
The "policy" for the validity of a block is codified.
It's still determined by people (which is the hullabaloo about BitcoinXT and block size being debated now in Hong Kong) but it's a world of "one-CPU one-vote", meaning if the majority of mining power agrees that these are the rules, then those are the rules and they'll continue mining.
Bitcoin itself is just one particular use of this idea of "a chain of blocks" proving that a certain amount of hard work was done to get to that state.
Altcoins (as mentioned in a comment above) are just modifications of BTC, changing some parameters and the name, which is interesting, but unlikely to be as "mainstream" for the simple fact that most people with money in Bitcoin don't fully understand cryptocurrency in general. Some of these do really novel things (ie, Nu, which splits "currency" into one part used for investing and another used for transacting), but AFAIK they're not mainstream yet.
Back to Bitcoin and banks...
Bitcoin effectively allows everyone to act as their own bank. This is really cool (I was amazed when I could "send transactions" and see them show up on another computer without a central authority...), but it comes with it's own drawbacks like... if your wallet is stolen, there's no one to call and yell at (see https://bitcointalk.org/index.php?topic=83794.0)
Banks want a way to "be their own banks (in the modern way BTC does)" because right now they're centralized and rely on a lot of trust. This means that transactions are slow (ACH is super slow compared to the BTC block time) and can be reversed if enough people make a stink (see https://www.quora.com/If-my-bank-mistakenly-deposits-1-000-000-into-my-account-am-I-legally-allowed-to-spend-it-before-they-realize-their-mistake)
When banks talk about using the concept of a block chain, I don't think they're really thinking about currency in the way we think of USD, but rather a "better way to handle trading in an open and untrusted system".
In other words, banks are saying "We want a way to not trust each other, and still clear trades quickly and efficiently."
For example, I agree to trade you 1 share of GOOG for $700 USD, and I want that to happen quickly, reliably, irrevocably, and without me knowing or trusting you. Sounds kind of like a Bitcoin transaction, right?
Bitcoin is one way to do it, but that would mean the same currency you use to settle trades is the one you use to buy a cup of coffee -- which can cause issues. If banks just create their own currency that's used exclusively for trading, it's just an Altcoin with a very special purpose and very big backers.
That (I believe) is what SETLcoin (Goldman's idea) does (http://www.americanbanker.com/news/bank-technology/goldman-sachs-files-patent-for-cryptocurrency-system-setlcoin-1078153-1.html)
Well, I found the answer, in a interview with Digital Currency Group CEO Barry Silbert you can read about here: http://coinjournal.net/barry-silbert-on-why-private-permissioned-blockchains-will-fail/
Basically he says banks are too slow and don't cooperate well together.
“There’s a lot of talk; there’s a lot of interest, but anybody who has worked on systems at banks can tell you it takes two years to deploy any basic system. So, we’re five [to] ten years out from any of these efforts actually turning into a product that can be used, and while that’s happening, it is my belief that the Bitcoin blockchain is going to address a lot of the issues that were mentioned before around security and scalability. Ultimately, the innovation that’s going to happen, which will be adopted by the banks, is going to be done outside of the banks.”