We are all thinking that true mainstream adoption is needed for bitcoin's value to have big price levels but practically those big price levels ALONE will make mainstream adoption happening. Main stream adoption is NOT needed for reaching big values but for having sustaining values.
Now, based on how bitcoin had recovered from the 2018 downfall, it may test $1M levels in less than 18 months given that how intensively mainstream media may keep on inducing FOMO among all types of investors.
I believe bitcoin may test $100k levels before end of 2019. DO NOT ASK me any technical proof. Your FOMO will not obey any mathematical formula. Reach of awareness on the future of bitcoin is purely random hence I am not involving any analysis for this speculation but based on how bitcoin prices had traded in the past and where it is right now.
Already LIBRA, BAKKT and various ETFs are doing enough media things to spread words on cryptos and bitcoins. These (and other related positive news like Wall street listing bitcoin futures etc.) will result in RECURSIVE FOMO which is all, we need. By mid of 2020, we are about to experience another halving which will be the finisher-catalyst to test $1M before end of 2020.
Finally, in my speculation bitcoin may value $1 Billion in next few decades but before that get ready for experiencing many roller-coaster rides.