No one in their right mind is going to use BTC as a currency as long as they expect the value to keep rising.
You know your cash will be worth less this time next year, thats the incentive to spend it.
In the 19th century, during the golden standard, there was a constant deflation. So what? Why spend gold and silver, if you can buy more for them next year? Because you need to eat today!
That's OK while you can go out and earn more to pay for tomorrow, even if it will earn slightly less. But that's not where Bitcoin is, unless you invest a large $ (or BTC) in a ASIC which will be redundant in a couple of months. If you dont hold, you are paying increasing amounts to buy, if you hold you are compelled to hold longer to benefit from deflation making your asset worth more. This is an drawback that pro-deflation advocates ignore. Once it didn't matter because you could just mine more, I fear the shift to ASIC is actually counter productive.