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Given the halving of new supply and increased demand, $20k is definitely within reach for 2020. Perhaps higher. During the previous halvings, it wasn't instant, but took months to a year. No complaints here for sure.
I may be wrong, but in my opinion newly mined BTC is not "supply", in the market sense of the word. "Supply" is the amount people are willing to sell. It can exceed the amount of newly mined Bitcoin many times, or, theoretically, it can be less than that, if miners prefer to hold instead of cashing out right away. Each time the halving may become less significant if the price stays in the same ballpark, but so far it hasn't.
In other words, even if halving does affects the "supply", it does so to a very limited extent.
That is why I specifically said "new supply" - which you highlighted. :-) When you decrease the new supply on the market you certainly decrease the amount that miners are able to sell, whether or not they do so immediately or not. That decreases the overall "supply" that is available to be sold on the market.
It is critical to note that prices are set at the margin so a small decrease in overall supply due to a decrease in new supply, can have an outsized impact on price. Particularly if demand stays constant or increases. Similarly a small increase in demand can have an outsized impact on price when supply is constant or decreasing. Now with bitcoin, everyone knows that the eventual total number of bitcoins is fixed (barring any overflow bugs), new supply is decreasing, the only question is at what price, if any, person X is willing to sell.
Obviously it is all complex, but miners do often have to sell at least some supply to cover costs. Going to 900/day from 1800/day becomes significant over time just to pay the bills and they have 900 fewer per day to sell to cover costs -- at current prices 900/per day is around US$10-$11 million per day, or around US$4 billion per year in fewer newly mined coins available. With demand from GBTC reportedly soaking up a large percentage of newly minted/mined coins back in the spring, cutting that in half seems bound to impact price. Back in 2012, a decrease from 7200 to 3600/day didn't cost that much if the price was US$5-10, maybe $30000-$40000 per day.
Nothing is guaranteed, but the past 2 halvings have had a large impact on price. Increased or constant demand and less "new supply" seem to be a recipe for a higher fiat price. (Speaking of fiat, printing an extra US$5-10 trillion for coronavirus aid should make people aware of the dangers of fiat inflating purchasing power away).
:-)