There is a huge psychological barrier between the 17-20k mark. In order for it to reach 50k people will have to not sell off most of their BTC when it reaches that mark and also buy in DESPITE what happened just a few months ago. Consider all the people who currently regret not selling their BTC back in December who could have retired on their initial BTC investment? On top of that, the people who bought in at or near the ATH thinking it was mooning to 30K and beyond and will sell as soon as they can recoup their investment and thank their lucky stars they didn't go bankrupt. Id expect a major dip if it hits 17-20k in my opinion, maybe even a panic sell that drops it by as much as 10k in as little as a couple days. At the 15k mark I would expect a ton of volatility and it will begin to clean out some of the weaker hands.
Also remember some mysterious entity bought 400m worth of BTC when it was at 10k, if it hits 15k and they sell between 15-17k, they are set to make 250m on a 400m investment in as little as a few months. This is assuming they are not a long term holder of course. We have no clue what their intentions are but with that kind of buying/selling power, they could easily be manipulating the market and basically just doing a pump/dump of BTC.
Im only approaching this from a psychological perspective though. Im not a professional trader, this is just something to watch out for as BTC prices go up and we near these price points.