There will be some alt-coins that will survive, but again not because they present any sort of transaction-like competitive advantages. Traditional banks will win this transaction war, there is no doubt in my mind that Bitcoin will not win a transaction war. Banks, PayPals, Amazons, Apples all won't sit idly and watch crypto-like currencies eat into their mainstream revenue. In five years, transactions for banks will be good-enough that the average consumer moving into bitcoin won't make sense for their financial systems will be good enough.
Banks' technical capabilities might reach global reach (but I very much doubt that too), but they have an insurmountable problem. The governments are going to institute capital controls in order to trap wealth and tax it to death as the global economic implosion proceeds. Ditto war is rising and trading with the enemies' citizens will not be allowed on the official banking systems (note the recent sanctions against Russia). Here look how bad it is getting already with HSBC.
And I see they have no prayer of supporting the volume of tiny micro payments any time soon (VISA only sales to 6000 txs per second now), nor getting significant penetration into all NICs emerging markets. Here where I am, if someone in the grocery lane is holding a card instead of cash, I run to the next queue because it adds about 5 minutes delay to the transaction. The derelict card readers are only at every 3rd register (some broke or don't work or timeout over and over) and it just isn't well integrated into the POS here. And this is at ShoeMart mall, which is the largest and one of the most modern mall chains in the country which also has malls in China. Hong Kong has a very efficient electronic swipe payment system used by most of the population there. But this is not in every country in the world.
You can argue this doesn't affect the mainstream, but who is left to hold up the F.U.B.A.R. global economy if we rely on the oblivious n00bs who are sucking the tit of social welfare and
Possibly the only real economy standing will be ours. Or if the banks can keep 80% market share of that demographic which is 20% of productivity = 0.8 x 0.2 = 16% GDP share. We will take 20% market share of that demographic which is 80% of productivity = 0.2 x 0.8= 16% GDP share.
If the socialism overshoots into the abyss, then the banks can take 80% of 0% productivity.
Also I don't assume we can't do transactions better than they can. We have to learn how to play to our decentralized advantage. I think we will find ways, but my logic doesn't depend on it. For example, how will Paypal ever stop fraud wherein someone reversed the charge on 2 BTC I sold them? Banks don't trust each other, and that fragmentation will get worse not better. As the global economy gets worse, fraud and theft is going to skyrocket. Banks are going to be stealing from their depositors with bail-ins. Who the hell is going to trust a bank? Mt.Gox is an early indicator of what is coming to every bank near you.
As for transaction speed, I think it is technically possible to get to 30 seconds or lower with decentralized proof-of-work crypto-currency. The technical issue is orphan rate.
Bitcoin does not need mainstream adoption, it doesn't need even a fraction of the general population to be wildly valuable. Bitcoin will grow on greed and speculation alone for a long time to come. It is enough for penny stocks, internet boom 1.0, precious metals, and countless other speculative assets, it will be enough for Bitcoin. Transactions only serve as the ultimate excuse for governments to allow it to live. Transactions are only the secret protection that allows Bitcoin to live wave after wave of speculative bubble.
Greed and speculation alone are enough to propel Bitcoin to 250 billion dollars or more.
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I also estimate around $10,000 is roughly the top for Bitcoin. Might reach $50,000 at most, but that is less likely.