Those seem pretty unpredictable to me.
Deflation is regressive - it harms those who need to spend the most and leads to concentration of capital at the expense of labour. It punishes those with debt, which will make it difficult for normal people to ever acquire large capital goods e.g. a house (by the way your argument that lenders won't mind negative interest rates because their final value is worth more than what they started with is wrong because it doesn't take into account opportunity cost - lenders compare the returns not against the current value of their holdings, but against their other options e.g. putting the money in a hole). It reduces the velocity of money and therefore economic output. You say that at least it redirects it to the areas that are most important, which may be true, but nevertheless, it shrinks the pie from which we all partake, and reduces the rate of growth, a problem in a world with a growing population. Bitcoin would also suffer from similar problems to gold in that in bad economic times, all the capital needed to recover would flee the regions suffering, making any recovery much more difficult.
> It reduces the velocity of money and therefore economic output
You would have to explain how exactly this happens. Output != value. If you dig holes or build cars no one buys you increase output, but you don't add value to the economy.
Deflation means no new money that doesn't come from someone else's stash. Which means the money can only come from the rich.
Except, the rich's money is increasing in value. So they spend proportionally less and less of their true wealth, while creating no value, to buy the necessities of life from the poor.
And the poor, despite producing real value (food, cars, yachts, factories), no matter how hard they work, can never be wealthier then the established rich.
It's social stratification by absolutes, fortunately it usually doesn't last since the disenfranchised 99% by definition outnumber the 1%.
But let's briefly reexamine it again... What does happen to bitcoin if no one spends it? Well it probably goes to a value of $0. Is this a hard inference? That makes your comment kind of reduce to "you ignored the problem of what happens if bitcoin dies." If it dies, your coins are worthless. Duh? In reality we see people are spending bitcoins so there is presently some sort of incentive to spend, so maybe the problem isn't the lack of incentive to spend itself, but whatever causes that lack of incentive to spend in the first place, and that cause cannot be currently at work because currently there is incentive to spend. So the cause cannot merely be "deflation", as that's already happening. A future cause could be hyper-deflation, but then I'll ask you what happens to the USD in hyper-inflation...
A more general thing to look at is the incentive to use bitcoin and ask whether bitcoin is useful. Bitcoin is more than just a currency, it's also a set of tools for making transactions. If bitcoin isn't useful, there's no incentive to spend or hoard it. Presently I think bitcoin is useful; bitcoin has the pretty cool feature of being able to pseudonymously send an arbitrary amount of money from anywhere in the world to anywhere else in the world, instantly, without reliance on a single third party. And the stuff highlighted on https://en.bitcoin.it/wiki/Contracts and elsewhere for future applications that the core infrastructure is more or less ready to handle is very cool. And there are items or experiences one can acquire with bitcoin that are difficult to acquire with traditional currencies and financial systems. All of these features are subject to competition. The US government could make drugs and online gambling legal and vendors could make such items and experiences easy to acquire with USD, Visa et al. could stop charging their array of fees (at least with bitcoin the only fees are small not-percentage-based transaction fees and currency exchange fees that are typically less than credit card processing percentages), PayPal could get better, etc. The many ways in which bitcoin could die due to better competition make that threat much more interesting and plausible to consider and wonder whether bitcoin could keep up or would die immediately as the case would be for "what if it dies because no one spends it anymore?".
Edit: Admittedly a more interesting question can be "what's likely for the future of bitcoin when considering the ratio between people who find bitcoin useful for its features vs. people who just find it useful as a way to get more USD?" If this was what you really meant to highlight, I'm sorry for misinterpreting.
LOL, seriously? With slot machine you are guaranteed to loose statistically. Bitcoin is very different bet. No one can calculate what the probabilities are for different outcomes when it comes to Bitcoin.
Do either enough times and you'll most likely whittle your money away. But you could win big with a few spins or a few lucky trades.
The value has been going up dramatically during the last few years pretty consistently and demand is steadily rising.
Bitcoin is gaining popularity in China quickly and they trade quite some volume on the exchanges now.
If tomorrow the USA gets together with China and Russia and persuades the entire world to outlaw Bitcoin, with the threat of a heavy punishment for anyone trading in Bitcoin, the value of Bitcoin will crash, probably very close to 0. In this scenario (which is not all that far-fetched) absolutely everyone loses, hence not a zero sum market.
If you and I agree that we each own a million fake dollars, we don't actually lose anything when later we decide we aren't.