However, I very much doubt that even if $5.9k or within that vicinity proves to be the bottom that we'll see major bullish developments in the second half of the year.
The bearish sentiment is still strong within the market and a huge trend reversal seems unlikely at the moment. Even if the recovery starts, it'll be a gradual process that will see small increases every time, not anything absurd like last year that you're suggesting. An ATH is pretty much impossible even in the event of a recovery both this year and 2019, imho.
That is also what I am expecting that we cannot witness the parabolic run like in 2017 winter at this time. The rise will be gradual and it will take a long time to people to realize that we are in the bull mode. If we hit ATH then it would be great but I would also be happy if BTC reach $13k level this year, and that would be "realistic ATH" for this year.