While I think it will probably be lacklustre for most of 2019. I don't think it will take years for a bull run.
For bottom of bitcoin, we probably have already hit it at 3k. Possibly could head lower to 2kish but I really dont see any lower than that. 2nd half of 2019 should see most coins picking up steam.
As to when it will be 20k again. 2020 is a strong possibility with btc halvening. I could see another euphoric run in 2021 with btc possibly hitting 100k.
It's definitely possible and anything can happen because nobody really knows what the market is going to do. There is a lot of fear and doubt going on right now as you can tell by some of the comments in here from people who have no idea what's going to happen, or have any idea about how Bitcoin works.
When you read news articles about companies finding ways to impliment it in their technology, and people finding more uses for it, now wall street wanting a piece of the action. And when it goes back up, all these people spreading fear and doubt will probably jump on board and help it go even higher...