My opinion:
First, BTC will be a investment vehicle. The inflationary dollar will cause individuals with many assets to diversify some of that into BTC due to a rapidly declining dollar value, causing BTC to go up in value at a relatively constant pace, albeit slower than the current rate of growth.
Sooner or later a big lender will figure out that BTC is a non-inflationary currency and, to effectively charge higher interest, they and will start offering online consumer BTC loans detached from traditional banking. This will cause a short term depression in price as the artificial supply created by the lending goes onto the market. "Normal" BTCers like me and other people here will promptly buy up a ton of BTC, and the borrowers will be in a position like a short-squeeze. This will guarantee their interest in obtaining BTC just to pay off their debts. They'll eventually figure out that they can get BTC cheaper if they're paid directly in it, so some will pressure employers to do just that.
Next, the BTC loans will cause lots of BTC to be spent in that period of time, bringing in huge revenue to BTC businesses. As these businesses grow, they'll prove that BTC can be a profitable model and this will encourage other business to switch over.
Thus, employers will both accept, and eventually pay out, BTC, thus making it a legitimate currency. This final bump is what will make the price really rocket.
So I don't think it will be any one of the things listed in the poll, but rather a merging focusing on the various advantages of BTC.
Good thinking. Of course, the borrowing in BTC might be of lower magnitude than current fiat borrowing for two reasons: The borrower can not profit from inflation, and the banks can not get hold of cheap BTC from the Fed.
Borrowers seldom think of inflation when borrowing, while lenders do. That's because lenders generally pay much more attention to the profitability of their business than their customers. As such, BTC is the natural currency to lend in,
if you can get a hold of it.
Second, I suspect that the borrower will likely either already have a ton of BTC ready to lend, or gather the support of people with lots of BTC. Imagine something like Just-Dice. Just-Dice's business is dubious at best and yet it has over 60k BTC invested. Imagine if a similar pool was created after BTC had increased in price to $250. That's over $15 million dollars worth of BTC to lend. That's plenty for such a lender to make consumer loans.