There is no doubt that 2018 will be interesting year and that price of BTC will not have a lot of ups and downs,it is actually one of the features BTC have over the years.Since BTC is decentralized digital currency we should not expect volatility may be something that will disappear in the future,it is very possible that it will become even bigger.
Some say that it will be hard to manipulate the market due high market cap,but I think that people who have lot of BTC increase their supply with time and also start to work together to move market in the desired direction.At the end of the day for most people involved in cryptocurrency the only thing that matters is profit.
I agree with your points regarding manipulation of those with large quantities of BTC, and how while many have said Market cap will act as a insulator to high volatility, we just arent there yet.
Bitcoin alone didn't broach $400 Billion (crypto as a whole hit $800 on it's peak). The Russel 3000 (basically all US Stocks) is roughly 30 Trillion. And we've seen (as we did in 2008), a market that is roughly 100 years old; tumble in half, literally with the Dow landing in the 6000 range. But look where it is now.
Bitcoin is basically like a large company in the overall stock market, that has grown so rapidly in such a short timespan, a correction was inevitable.
Long term, I think one would be foolish to think that Bitcoin is not here to stay. That it's user base will grow. That younger generations will accept it and embrace it, and that it will become a huge market force in the global economy.
Add to that, the next bitcoin halving.
To not think that Bitcoin has enormous growth potential would be foolish.
But as Lucius stated, there will be manipulation; especially considering how unregulated exchanges are, some allowing 100:1 leveraged trading (just reckless in my opinion); but with those types of margin allowances; a person with just 100 BTC has enormous power and market influence.
Once the market cap does grow larger, which it will; Bitcoin will reach $20,000 again, then $50,000, I believe well into the six figures, the only question, what day will that be; and introduce more regulation; or at least regulation which hampers reckless market trades, such as the 100:1 positions people make, I think we will see less volatility; increased adoption, and more companies, not just individuals seeing BTC for what it really is... a tool and technology which will change the world and the way money is used moving forward.