I will gladly accept his BTC from 2009 and give him USD from 2009 for the 2009 price.
Sorry, but stability is not holy grail in itself. I would prefer constant supply to it for long term store of value
However, I think if I had a reliable income that was measured and paid out in BTC, then the answer would be yes.
That's really the benchmark for when BTC can be used as a proper currency, when people are prepared to set their value in BTC.
At the moment it makes a decent transfer mechanism for funds where the quantity is calculated relative to another currency at the time of transfer.
If Bitcoin were to become a standard currency it will necessarily have to go though more volatility. Bitcoin's value, should it succeed, is significantly higher than where it is now (conversely, should it fail, lower). When its value does not match its utility it must eventually move. Stability increases utility. These oppossing forces will cause occilations like a plucked string. The occilations should deminish over time as the forces reach equilibrium. The point of balance is anyone's guess right now.
I think you haven't thought it through if you still think that. 2BTC is currently worth just over 2g in dollars. In 10 years time, it might be worth 10g in dollars or it might be worth 4g in dollars. You'd be crazy to agree to pay 2BTC a month for 30 years with a currency that doesn't have a predictable future value. The dollar has a predictable future value; stability is not about not losing value, it's about predictable value.
> That's really the benchmark for when BTC can be used as a proper currency, when people are prepared to set their value in BTC.
No, people can do that now, but they do it in relation to exchange rates of more stable currencies. BTC will be usable as a proper currency only when its future value becomes somewhat predictable, predictable enough to denominate long term contracts like mortgages in it without relation to another currencies exchange rate. It'll take decades to reach that point.
A currency without a reasonable long term predictable value, isn't a currency, it's a commodity.