Great post. I think the answer is in what you have stated .... the volatility. Based on that, the simple answer is NO. Bitcoin can never be currency as it currently is, no more than oil, gold, silver or pork bellies. Think about it,  buying something for 1 bitcoin 7 months ago equaled roughly $20,000. That same item would cost about 3 bitcoins now or $60,000 end of 2017 prices.. It fails on all 3 measures you mentioned, medium of exchange, store of value, unit of account.

Bitcoin is a means of wealth transfer, no more no less.

The only value Bitcoin has is still measured against real currency such as US dollars. Unless you expect the value of Bitcoin to drop vs USD no-one should be buying anything using bitcoin. Also, if I expected the value of bitcoin to rise, as a seller I would definitely accept Bitcoin as payment to take advantage of uninformed buyers. Seems the sellers are losing now, but that will change because this is still a young market and bitcoin has a long way to rise.